codes_cn_final

Program 1:OSI Model
Source Code:
#include<stdio.h>
#include<conio.h>
void main()
{
printf("\n \t\t ISO-OSI Model");
printf("\n LAYERS Sender Side");
printf("\n APPLICATION lAYER !! AH !!DATA!!");
sleep(1);
printf("\n PRESENTATION lAYER !! PH !!AH!!DATA!!");
sleep(1);
printf("\n SESSION LAYER !! SH !!PH!!AH!!DATA!!");
sleep(1);
printf("\n TRANSPORT LAYER !! TH !!SH!!PH!!AH!!DATA!!");
sleep(1);
printf("\n NETWORK LAYER !! NH !!TH!!SH!!PH!!AH!!DATA!!");
sleep(1);
printf("\n DATALINK LAYER !! DH !!NH!!TH!!SH!!PH!!AH!!DATA!! CRC !!");
sleep(1);
printf("\n PHYSICAL LAYER 100100101010101110001010010 \n");
sleep(1);
printf("\n LAYERS Recevier Side");
printf("\n PHYSICAL LAYER 100100101010101110001010010 ");
sleep(1);
printf("\n DATALINK LAYER !! DH !!NH!!TH!!SH!!PH!!AH!!DATA!! CRC !!");
sleep(1);
printf("\n NETWORK LAYER !! NH !!TH!!SH!!PH!!AH!!DATA!!");
sleep(1);
printf("\n TRANSPORT LAYER !! TH !!SH!!PH!!AH!!DATA!!");
sleep(1);
printf("\n SESSION LAYER !! SH !!PH!!AH!!DATA!!");
sleep(1);
printf("\n PRESENTATION lAYER !! PH !!AH!!DATA!!");
sleep(1);
printf("\n APPLICATION lAYER !! AH !!DATA!!");
sleep(1);
}
Output Screen Snapshot:




Program 2:Bit Stuffing
Sorce Code:
#include<stdio.h>
#include<conio.h>
main()
{
int a[15];
int i,j,k,n,c=0,pos=0;
printf("\n Enter the number of bits:");
scanf("%d",&n);
printf("\n Enter the bits:");
for(i=0;i<n;i++)
scanf("%d",&a[i]);
for(i=0;i<n;i++)
{
if(a[i]==1)
{
c++;
if(c==5)
{
pos=i+1;
c=0;
for(j=n;j>=pos;j--)
{
k=j+1;
a[k]=a[j];
}
a[pos]=0;
n=n+1;
}
}
else
c=0;
}

printf("\n DATA AFTER STUFFING \n");
printf(" 01111110 ");
for(i=0;i<n;i++)
 {
printf("%d",a[i]);
}
printf(" 01111110 ");
getch();
}
Output Screen Snapshot:

Program 3:Byte Stuffing
Source Code:
#include<stdio.h>
#include<conio.h>
void main()
{
char frame[100],str[50][50];
char flag='z';
char esc='x';
int i,j,k=0,n;
frame[k++]='z';
printf("Enter no.of String ::\t");
scanf("%d",&n);
printf("Enter String :");
for(i=0;i<=n;i++)
  {
gets(str[i]);
  }
printf("You entered ::\n");
for(i=0;i<=n;i++)
   {
puts(str[i]);
   }
printf("\n");
for(i=1;i<=n;i++)
  {
for(j=0;j<strlen(str[i]);j++)
      {
    if(str[i][j]!=flag&&str[i][j]!=esc)
    {
        frame[k++]=str[i][j];
    }
    else{
        frame[k++]='x';
        frame[k++]=str[i][j];
    }
      }
  }

frame[k++]='z';
frame[k++]='\0';
printf("------------------------------\n");
printf("Byte stuffing at sender side:\n\n");
printf("------------------------------\n");
for(i=0;i<k;i++)
  {
printf("%c",frame[i]);
  }
printf("\n------------------------------");
printf("\nByte stuffing at receiver side\n\n");
printf("------------------------------\n");
for(i=0;i<k;i++)
  {
if(frame[i]=='x'|| frame[i]=='z')
     {
i++;
     }
printf("%c",frame[i]);
  }
getch();
}
Output Screen Snapshot:


Program 4:Character Count
Source Code:
#include<stdio.h>
#include<conio.h>
#include<string.h>
void main()
{
int i,j,k,n,c=0,l;
char s[20];
printf("Enter the string:");
gets(s);
l=strlen(s);
printf("\n%d",l);
printf("\n\n");
j=0;
printf("Enter the frame size:");
scanf("%d",&n);
k=l/n;
for(i=0;i<k;i++)
{
printf("\t dlestx");
while(j<l)
{

putchar(s[j]);
c++;
j++;
if(c==n)
break;
}
printf(" dlestx \t");
printf("\n\n");
c=0;
}
}

Output Screen Snapshot:


Program 5:CRC
Source Code:
#include<stdio.h>
#include<string.h>
#define N strlen(g)

char t[28],cs[28],g[]="10001000000100001";
int a,e,c;

void xor(){
    for(c = 1;c < N; c++)
    cs[c] = (( cs[c] == g[c])?'0':'1');
}

void crc(){
    for(e=0;e<N;e++)
        cs[e]=t[e];
    do{
        if(cs[0]=='1')
            xor();
        for(c=0;c<N-1;c++)
            cs[c]=cs[c+1];
        cs[c]=t[e++];
    }while(e<=a+N-1);
}

int main()
{
    printf("\nEnter data : ");
    scanf("%s",t);
    printf("\n----------------------------------------");
    printf("\nGeneratng polynomial : %s",g);
    a=strlen(t);
    for(e=a;e<a+N-1;e++)
        t[e]='0';
    printf("\n----------------------------------------");
    printf("\nModified data is : %s",t);
    printf("\n----------------------------------------");
    crc();
    printf("\nChecksum is : %s",cs);
    for(e=a;e<a+N-1;e++)
        t[e]=cs[e-a];
    printf("\n----------------------------------------");
    printf("\nFinal codeword is : %s",t);
    printf("\n----------------------------------------");
    printf("\nTest error detection 0(yes) 1(no)? : ");
    scanf("%d",&e);
    if(e==0)
    {
        do{
            printf("\nEnter the position where error is to be inserted : ");
            scanf("%d",&e);
        }while(e==0 || e>a+N-1);
        t[e-1]=(t[e-1]=='0')?'1':'0';
        printf("\n----------------------------------------");
        printf("\nErroneous data : %s\n",t);
    }
    crc();
    for(e=0;(e<N-1) && (cs[e]!='1');e++);
        if(e<N-1)
            printf("\nError detected\n\n");
        else
            printf("\nNo error detected\n\n");
            printf("\n----------------------------------------\n");
        return 0;
}
Output Screen Snapshot:

Program 6:Sliding Window Protocol
Source Code:
#include<stdio.h>
#include<conio.h>
void main()
{
char sender[50],receiver[50];
int i,winsize;
 printf("\n ENTER THE WINDOWS SIZE : ");
scanf("%d",&winsize);
 printf("\n SENDER WINDOW IS EXPANDED TO STORE MESSAGE OR WINDOW \n");
 printf("\n ENTER THE DATA TO BE SENT: ");
fflush(stdin);
gets(sender);
for(i=0;i<winsize;i++)
receiver[i]=sender[i];
receiver[i]=NULL;
 printf("\n MESSAGE SEND BY THE SENDER:\n");
 puts(sender);
 printf("\n WINDOW SIZE OF RECEIVER IS EXPANDED\n");
 printf("\n ACKNOWLEDGEMENT FROM RECEIVER \n");
for(i=0;i<winsize;i++);
printf("\n ACK:%d",i);
 printf("\n MESSAGE RECEIVED BY RECEIVER IS : ");
 puts(receiver);
 printf("\n WINDOW SIZE OF RECEIVER IS SHRINKED \n");
}

Output Screen Snapshot:


Program 7:Hamming Code
Source Code:
#include<stdio.h>
#include<math.h>
int main()
{
     int a[20],b[20],c[20],d[20],i,k,m,f,n,j,r,p,x,y,z,ch,key,q,v,sum=0;
     system("clear");
     printf("\n ENTER THE LENGTH OF DATA WORD :");
     scanf("%d",&k);
     printf("\n ENTER THE DATA WORD \n");
     for(i=1; i<=k; i++){
           scanf("%d",&a[i]);
     }
     m=1;
     while((k+m+1)>=pow(2,m)){
           m++;
     }
     printf("\n Value of m is : %d",m);
     n=k+m;
     j=1; r=0;
     for(i=1; i<=n; i++){
           p=pow(2,r);
           if(i==p){
                b[i]=0;
                r++;
           }
           else{
                b[i]=a[j];
                j++;
           }
     }
     printf("\n INTERMEDIATE CODE WORD IS \n");
     for(i=1; i<=n; i++)
           printf("%d",b[i]);
     p=0;
     for(i=1; i<=m; i++)
     {
           x=pow(2,p); r=1;
           for(j=x; j<=n; j=j+(x*2)){
                for(y=j; y<(j+x); y++){
                     c[r]=b[y];
                     r++;
                }
           }
           z=0;
           for(y=1; y<=(r-1); y++)
           {
                if(c[y]==1) z++;
           }
           if(z%2==0)
                b[x]=0;
           else
                b[x]=1;
           for(y=1; y<=20; y++)
                c[y]=0;
           p++;
     }
     printf("\n\n THE HAMMING CODE IS \n");
     for(i=1; i<=n; i++)
           printf("%d",b[i]);
     while(1){
                printf("\n\n PRESS 1 TO ALTER A BIT 0 to EXIT \n\n");
                scanf("%d",&ch);
                if(ch==1){
                        printf("\n ENTER THE BIT YOU WANT TO CHANGE \n");
                        scanf("%d",&key);
                        for(i=1; i<=n; i++){
                                if(i==key){
                                        if(b[key]==1) b[key]=0;
                                        else b[key]=1;
                                        break;
                                }
                        }
                        printf("\n THE NEW CODE IS \n\n");
                        for(i=1; i<=n; i++)
                                printf("%d",b[i]);
                }
                else
                        break;
        }
     p=0; q=0;
        for(i=1; i<=m; i++)
        {
                x=pow(2,p); r=1;
                for(j=x; j<=n; j=j+(x*2)){
                        for(y=j; y<(j+x); y++){
                                c[r]=b[y];
                                r++;
                        }
                }
                z=0;
                for(y=1; y<=(r-1); y++)
                {
                        if(c[y]==1) z++;
                }
                v=z%2;
           d[q]=v;
           sum=sum+(v*pow(2,q));
           q++;
                for(y=1; y<=20; y++)
                        c[y]=0;
                p++;
        }
     if(sum==0)
           printf("\n\n NO ERROR FOUND....... \n\n");
     else
           printf("\n\n ERROR AT POSITION %d",sum);
     printf("\n");
     return 0;
}
Output Screen Snapshot:


Program 8 : CHECKSUM
Source Code:
#include<stdio.h>
#include<conio.h>
#include<math.h>
void main()
{
int r,t[20],x,o,a[30],i,j,k,z,aa,b[20],n,y,s,n1,flag=0;
printf("*********sender side***********\n");
printf("enter the data length:");
scanf("%d",&n);
for(i=1;i<=30;i++)
{
a[i]=0;
}
printf("enter the data:");
for(i=1;i<=n;i++)
scanf("%d",&a[i]);
printf("enter the chopping size:");
scanf("%d",&o);
z=0;
for(i=1;i<=n;i=i+o)
{
x=o-1;
k=0;
for(j=i;j<i+o;j++)
{
 k+=pow(2,x)*a[j];
 x--;
}
z=z+k;
}
printf("\ntotal in decimal is=%d",z);
y=0;
s=1;
while(z>=1)
{
aa=z%2;
t[s]=aa;
s++;
z=z/2;
y++;
}
if(y>o)
{
t[1]=t[o+1]+t[1];
}
r=1;
for(i=o;i>=1;i--)
{
b[r]=t[i];
r++;
}
for(i=o;i>=1;i--)
{
if(b[i]>1)
{
b[i]=b[i]%2;
b[i-1]+=1;
}
}
printf("\nb[i]=");
for(i=1;i<=o;i++)
printf("\t%d",b[i]);
for(i=1;i<=o;i++)
{
if(b[i]==0)
b[i]=1;
else
b[i]=0;
}
printf("\nthe checksum value is:");
for(i=1;i<=o;i++)
{
printf("\t%d",b[i]);
}
printf("\n*********Receiver side*********\n");
for(i=1;i<=30;i++)
{
a[i]=0;
}
n=n+o;
printf("enter the data:");
for(i=1;i<=n;i++)
scanf("%d",&a[i]);
z=0;
for(i=1;i<=n;i=i+o)
{
x=o-1;
k=0;
for(j=i;j<i+o;j++)
{
 k+=pow(2,x)*a[j];
 x--;
}
z=z+k;
}
printf("total in decimal is:%d",z);
y=0;
s=1;
while(z>=1)
{
aa=z%2;
t[s]=aa;
s++;
z=z/2;
y++;
}
if(y>o)
{
t[1]=t[o+1]+t[1];
}
r=1;
for(i=o;i>=1;i--)
{
b[r]=t[i];
r++;
}
for(i=o;i>=1;i--)
{
if(b[i]>1)
{
b[i]=b[i]%2;
b[i-1]+=1;
}
}
printf("\nb[i]=");
for(i=1;i<=o;i++)
printf("\t%d",b[i]);
for(i=1;i<=o;i++)
{
if(b[i]==0)
b[i]=1;
else
b[i]=0;
}
printf("\nthe checksum value is:");
for(i=1;i<=o;i++)
{
printf("\t%d",b[i]);
}
for(i=1;i<=o;i++)
{
if(b[i]==1)
{
flag=1;
}
}
if(flag!=0)
printf("\nError present in the code....");
else
{
printf("\nNO error present in the code....");
getch();
printf("\n\tcode successfully accepted by receiver.....");
}
getch();
}

14BCE0728
SHREEJIT VERMA

8. Chat application using TCP/IP.

//client side

#include<stdio.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<netdb.h>
#define SERV_TCP_PORT 5035
int main(int argc,char*argv[])
{
int sockfd;
struct sockaddr_in serv_addr;
struct hostent *server;
char buffer[4096];
int k=5,cnt=0;
sockfd=socket(AF_INET,SOCK_STREAM,0);
serv_addr.sin_family=AF_INET;
serv_addr.sin_addr.s_addr=inet_addr("127.0.0.1");
serv_addr.sin_port=htons(SERV_TCP_PORT);
printf("\nReady for sending...");
connect(sockfd,(struct sockaddr*)&serv_addr,sizeof(serv_addr));
while(cnt <= k)
{
printf("\nEnter the message to send\n");
printf("\nClient: ");
fgets(buffer,4096,stdin);
write(sockfd,buffer,4096);
printf("Serverecho:%s",buffer);
printf("\n");
cnt++;
}
close(sockfd);
return 0;
}

//Server Side

#include<stdio.h>
#include<netinet/in.h>
#include<netdb.h>
#include<string.h>
#define SERV_TCP_PORT 5035
int main(int argc,char**argv)
{
int sockfd,newsockfd,clength;
struct sockaddr_in serv_addr,cli_addr;
char buffer[4096];
//creating a socket
sockfd=socket(AF_INET,SOCK_STREAM,0);

serv_addr.sin_family=AF_INET;
serv_addr.sin_addr.s_addr=INADDR_ANY;
serv_addr.sin_port=htons(SERV_TCP_PORT);
printf("\nStart");
//bind the socket to port address and any local interface
bind(sockfd,(struct sockaddr*)&serv_addr,sizeof(serv_addr));
printf("\nListening...");
printf("\n");
listen(sockfd,5);
clength=sizeof(cli_addr);
newsockfd=accept(sockfd,(struct sockaddr*)&cli_addr,&clength);
//newsockfd=accept(sockfd,(struct sockaddr*)NULL,NULL);
printf("\nAccepted");
printf("\n");
while(1)
{
bzero(buffer,4096);
read(newsockfd,buffer,4096);
printf("\nClient message:%s",buffer);
write(newsockfd,buffer,strlen(buffer)+1);
printf("\n");
}
//close(sockfd);
//return 0;

}








Ques. Simulation of Sliding Window Protocol

Simulation of Sliding Window Protocol
/* Simulation of Sliding Window Protocol */
#include<stdio.h>
#include<stdlib.h>
#include<string.h>

int main() {

  int win_size;
  int no_of_packets;
  int base = 0;
  int next_seq_no = 0;


  printf("Enter the window size: ");
  scanf("%d",&win_size);
  printf("Enter no of packets: ");
  scanf("%d",&no_of_packets);
  int *buffer = (int *)malloc(no_of_packets * sizeof(int));

  int i,j;
  printf("\nCurrent buffer:\n");
  for(i=0;i<no_of_packets; i++) {
    buffer[i] = i+1;
    printf("%4d",i+1);
  }

  j=0;
  int choice;
  while(base < no_of_packets) {
    j=0;
    printf("\nTransmitting packets:");
    while( ((base+j+next_seq_no) < no_of_packets) && (j+next_seq_no)<win_size )  {
      printf("%4d",buffer[base+j+next_seq_no]);
      j++;
    }

    printf("\nUnacknowledged packets: ");
    j=0;
    while( (base+j) < no_of_packets && j< win_size) {
      printf("%4d",buffer[base+j]);
      j++;
    }

    printf("\nEnter a packet no to acknowledge that packet or -1 to simulate timout event: ");
    scanf("%d",&choice);

    if(choice < 0) {
      printf("\nRetransmitting packets:");
      j=0;
      while( (base+j) < no_of_packets && j<win_size )  {
        printf("%4d",buffer[base+j]);
        j++;
      }
      next_seq_no = base+win_size;
    }
    else {
      next_seq_no = base+win_size-choice;
      base = choice;
    }
  }
  return 0;
}


OSI Model

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

int main()
{
    char msg[100];
    char temp[100];
    char ah[100]="AH ", ph[100]="PH", sh[100]="SH", th[100]="TH", nh[100]="NH", dh[100]="DH";
    char ahr[100], phr[100], shr[100], thr[100], nhr[100], dhr[100];
    printf("Enter your message is: ");
    scanf("%s",msg);
    printf("Transmitter:\n");
    strcpy(temp,msg);
    strcat(ah,temp);
    printf("Application Layer: %s\n",ah);
    strcpy(temp,ah);
    strcat(ph,temp);
    printf("Presentation Layer: %s\n",ph);
    strcpy(temp,ph);
    strcat(sh,temp);
    printf("Session Layer: %s\n",sh);
    strcpy(temp,sh);
    strcat(th,temp);
    printf("Transport Layer: %s\n",th);
    strcpy(temp,th);
    strcat(nh,temp);
    printf("Network Layer: %s\n",nh);
    strcpy(temp,nh);
    strcat(dh,temp);
    printf("DataLink Layer: %s\n",dh);
    strcpy(temp,dh);
    printf("%s",temp);
    printf("\nMessage reached to Physical Layer and ready to be transmitted.\n\n");
    printf("RECEIVER:\n\n");
    printf("Message entered into Physical Layer");
    int j,k,i=2;
    strcpy(dhr,temp);
    printf("\nDataLink Layer: ");
    printf("%s",dhr);
    printf("\nNetwork Layer: ");
    for(j=i,k=0;temp[j]!='\0';j++,k++)
    {
        nhr[k]=temp[j];
        printf("%c",nhr[k]);
    }
    i=i+2;
    printf("\nTransport Layer: ");
    for(j=i,k=0;temp[j]!='\0';j++,k++)
    {
        thr[k]=temp[j];
        printf("%c",thr[k]);
    }
    i=i+2;
    printf("\nSession Layer: ");
    for(j=i,k=0;temp[j]!='\0';j++,k++)
    {
        shr[k]=temp[j];
        printf("%c",shr[k]);
    }
    i=i+2;
    printf("\nPresentation Layer: ");
    for(j=i,k=0;temp[j]!='\0';j++,k++)
    {
        phr[k]=temp[j];
        printf("%c",phr[k]);
    }
    i=i+2;
    printf("\nApplication Layer: ");
    for(j=i,k=0;temp[j]!='\0';j++,k++)
    {
        ahr[k]=temp[j];
        printf("%c",ahr[k]);
    }
}




Frame Length


#include<iostream>
using namespace std;

int main()
{
     cout << "Enter the number of frames: ";
     int n;
     cin >> n;
     string str;
     string op;
     char size;
     while(n--)
     {
         cout << "Enter the word: ";
         cin >> str;
         size=(str.size())+'0';
         op = op + size + str;
     }
     cout << "The transmitted data is: \n";
     cout << op;
}




Hamming Code


#include<stdio.h>
#include<conio.h>
int main() {
    int data[7],rec[7],i,c1,c2,c3,c;
    printf("this works for message of 4bits in size \nenter message bit one by one:  ");
    scanf("%d%d%d%d",&data[0],&data[1],&data[2],&data[3]);
    data[6]=data[3]^data[2]^data[1];
    data[5]=data[2]^data[1]^data[0];
    data[4]=data[3]^data[2]^data[0];
    printf("\nthe encoded bits are given below: \n");
    for (i=0;i<7;i++) {
        printf("%d ",data[i]);
    }
    printf("\nenter the received data bits one by one: ");
    for (i=0;i<7;i++) {
        scanf("%d",&rec[i]);
    }
    c1=rec[1]^rec[2]^rec[3]^rec[6];
    c2=rec[0]^rec[1]^rec[2]^rec[5];
    c3=rec[0]^rec[2]^rec[3]^rec[4];
    c=c3*4+c2*2+c1 ;
    if(c==0) {
        printf("\ncongratulations there is no error: ");
    } else if( c==1)
    {
        printf("\n Error in 7th bit");
        if(rec[6]==1)
        rec[6]=0;
        else
        rec[6]=1;
    }
    else if(c==2)
    {
        printf("\n Error in 6th bit");
        if(rec[5]==1)
        rec[5]=0;
        else
        rec[5]=1;
    }
    else if(c==3)
    {
        printf("\n Error in 2nd bit");
        if(rec[1]==1)
        rec[1]=0;
        else
        rec[1]=1;
    }
    else if(c==4)
    {
        printf("\n Error in 5th bit");
        if(rec[4]==1)
        rec[4]=0;
        else
        rec[4]=1;
    }
    else if(c==5)
    {
        printf("\n Error in 4th bit");
        if(rec[3]==1)
        rec[3]=0;
        else
        rec[3]=1;
    }
    else if(c==6)
    {
        printf("\n Error in 1st bit");
        if(rec[0]==1)
        rec[0]=0;
        else
        rec[0]=1;
    }
    else if(c==7)
    {
        printf("\n Error in 2nd bit");
        if(rec[1]==1)
        rec[1]=0;
        else
        rec[1]=1;
    }
    printf("\n Corrected pattern\t");
        for (i=0;i<7;i++) {
            printf("%d ",rec[i]);
        }
    getch();
    return 0;
}





Bit Stuffing


#include <iostream>
using namespace std ;
int main ()
{

       char a[25] = "110011111100111111110";
       char b[25] = "", c[25] = "";
       int i = 0, count = 0, j = 0 ;

       cout << endl << "Before stuffing \t: " << a <<endl ;

       for ( i = 0, j = 0 ; a[i] ; i++, j++ )
       {
              if ( a[i] == '1' )
                     count++ ;
              else
                     count = 0 ;

              b[j] = a[i] ;

              if ( count == 5 )
              {
                     b[++j] = '0' ;
                     count = 0 ;
              }
       }

       cout << endl << "After stuffing  \t: " << b <<endl ;

       for ( i = 0, j = 0 ; b[i] ; i++, j++ )
       {
              if ( b[i] == '1' )
                     count++ ;
              else
                     count = 0 ;

              c[j] = b[i] ;

              if ( count == 5 )
              {
                     i++ ;
                     count = 0 ;
              }
       }

       cout << endl << "After de-stuffing  \t: " << c << endl << endl;
}


Byte Stuffing





#include <stdio.h>
#include <conio.h>
int main()
{
    char str[100];
    int k=0; int i,j;
    for(j=0;j<100;j++)
    str[j]=' ';
    printf("\n Enter length of data");
    scanf("%d", &k);
    printf("\n Enter data");
    scanf("%s",str);
    char flag='e';
    char ent='z';
    char temp;
    for (i=0;i<k;i++)
    {
        if(str[i]==flag)
        {
            for (j=k+1;j>=i+1;j--)
            {
                temp=str[j-1];
                str[j]=temp;
            }
            k++;
            str[i]='z';
            i++;
        }
        if(str[i]=='z')
        {
            for (j=k+1;j>=i;j--)
            {
                str[j]=str[j-1];
            }
            k++;
            str[i]='z';
            i++;
        }
    }
    for(i=k+1;i>=1;i--)
    {
        temp=str[i-1];
        str[i]=temp;
    }
    str[0]=flag;
    str[k+1]=flag;
    printf("\nOutput:");
    puts(str);
    getch();
}



Check Sum




#include<stdio.h>
#include<conio.h>
int adder( int binary1,  int binary2)
{
    int ad=0,sumer[20],i=0,remainder=0;
    while(binary1!=0||binary2!=0)
        {
         sumer[i++] = (binary1 %10 + binary2 %10 + remainder ) % 2;
         remainder = (binary1 %10 + binary2 %10 + remainder ) / 2;
         binary1=binary1/10;
         binary2=binary2/10;
        }
    if(remainder!=0)
       sumer[i++]=remainder;
    --i;
    while(i>=0)
    {
        ad=ad*10+sumer[i];
        --i;
    }
    return ad;
}
int main()
{
    printf("Enter the number of binary numbers for which you want to find the checksum \n");
    int count,rem=0,temp2=0;
    scanf("%d",&count);
    int temp;
    int sum=0;
    printf("Enter a binary number\n");
    scanf("%d",&temp);
    for(int i=2;i<=count;i++)
    {
        if(i==2)
        {
        printf("Enter a binary number\n");
        scanf("%d",&temp2);
        sum=sum+adder(temp2, temp);
        }
        else
        {
        printf("Enter a binary number\n");
        scanf("%d",&temp2);
        sum=adder(temp2, sum);
        }
    }
    printf("Sum=%d\n",sum);
    int newsum[100],c=0;
    for(int i=0;i<100;i++)
    newsum[i]=0;
    while(sum>0)
    {
        rem=sum%10;
        if(rem==0)
        {
        newsum[c]=1;
        }
        else if(rem==1)
        {
        newsum[c]=0;
        }
        c++;
        sum/=10;
    }
    c=c-1;
    printf("Checksum=");
    while(c>=0)
    {
    printf("%d",newsum[c]);
    c-=1;
    }
    return 0;
}



CRC Calculator



#include <stdio.h>
 #include <conio.h>
 #include <string.h>
 void main()
 {
 int i,j,keylen,msglen;
 char input[100], key[30],temp[30],quot[100],rem[30],key1[30];
 printf("Enter Data: ");
 gets(input);
 printf("Enter Key: ");
 gets(key);
 keylen=strlen(key);
 msglen=strlen(input);
 strcpy(key1,key);
 for(i=0;i<keylen-1;i++)
 {
 input[msglen+i]='0';
 }
 for(i=0;i<keylen;i++)
 temp[i]=input[i];
 for(i=0;i<msglen;i++)
 {
 quot[i]=temp[0];
 if(quot[i]=='0')
 for(j=0;j<keylen;j++)
 key[j]='0';
 else
 for(j=0;j<keylen;j++)
 key[j]=key1[j];
 for(j=keylen-1;j>0;j--)
 {
 if(temp[j]==key[j])
 rem[j-1]='0';
 else
 rem[j-1]='1';
 }
 rem[keylen-1]=input[i+keylen];
 strcpy(temp,rem);
 }
 strcpy(rem,temp);
 printf("\nQuotient is ");
 for(i=0;i<msglen;i++)
 printf("%c",quot[i]);
 printf("\nRemainder is ");
 for(i=0;i<keylen-1;i++)
 printf("%c",rem[i]);
 printf("\nFinal data is: ");
 for(i=0;i<msglen;i++)
 printf("%c",input[i]);
 for(i=0;i<keylen-1;i++)
 printf("%c",rem[i]);
 getch();
 }




Sliding Window




#include<stdio.h>

#include<conio.h> void main()
{

char sender[50],receiver[50]; int i,winsize;
clrscr();

printf("\n ENTER THE WINDOWS SIZE : ");

scanf("%d",&winsize);

printf("\n SENDER WINDOW IS EXPANDED TO STORE MESSAGE OR WINDOW \n"); printf("\n ENTER THE DATA TO BE SENT: ");
fflush(stdin); gets(sender); for(i=0;i<winsize;i++) receiver[i]=sender[i]; receiver[i]=NULL;
printf("\n MESSAGE SEND BY THE SENDER:\n");

puts(sender);

printf("\n WINDOW SIZE OF RECEIVER IS EXPANDED\n"); printf("\n ACKNOWLEDGEMENT FROM RECEIVER \n");
for(i=0;i<winsize;i++); printf("\n ACK:%d",i);
printf("\n MESSAGE RECEIVED BY RECEIVER IS : ");

puts(receiver);

printf("\n WINDOW SIZE OF RECEIVER IS SHRINKED \n");



getch();

}



Client server based Sliding window protocol



SENDER

#include<sys/socket.h>

#include<sys/types.h>

#include<netinet/in.h>

#include<netdb.h>

#include<stdio.h>

#include<string.h>

#include<stdlib.h>

#include<unistd.h>

#include<errno.h> int main()
{

int sock,bytes_received,connected,true=1,i=1,s,f=0,sin_size; char send_data[1024],data[1024],c,fr[30]=" ";
struct sockaddr_in server_addr,client_addr; if((sock=socket(AF_INET,SOCK_STREAM,0))==-1)
{

perror("Socket not created"); exit(1);
}



if(setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&true,sizeof(int))==-1)

{

perror("Setsockopt"); exit(1);
}

server_addr.sin_family=AF_INET; server_addr.sin_port=htons(17000); server_addr.sin_addr.s_addr=INADDR_ANY;
if(bind(sock,(struct sockaddr *)&server_addr,sizeof(struct sockaddr))==-1)

{

perror("Unable to bind"); exit(1);
}

if(listen(sock,5)==-1)

{

perror("Listen"); exit(1);
}

fflush(stdout); sin_size=sizeof(struct sockaddr_in);
connected=accept(sock,(struct sockaddr *)&client_addr,&sin_size); while(strcmp(fr,"exit")!=0)
{

printf("Enter Data Frame %d:(Enter exit for End): ",i); scanf("%s",fr);



send(connected,fr,strlen(fr),0); recv(sock,data,1024,0); if(strlen(data)!=0)
printf("I got an acknowledgement : %s\n",data); fflush(stdout);
i++;

}

close(sock); return (0);
}























RECEIVER

#include<sys/socket.h>

#include<sys/types.h>



#include<netinet/in.h>

#include<netdb.h>

#include<stdio.h>

#include<string.h>

#include<stdlib.h>

#include<unistd.h>

#include<errno.h> int main()
{

int sock,bytes_received,i=1; char receive[30];
struct hostent *host;

struct sockaddr_in server_addr; host=gethostbyname("127.0.0.1"); if((sock=socket(AF_INET,SOCK_STREAM,0))==-1)
{

perror("Socket not created"); exit(1);
}

printf("Socket created"); server_addr.sin_family=AF_INET; server_addr.sin_port=htons(17000); server_addr.sin_addr=*((struct in_addr *)host->h_addr); bzero(&(server_addr.sin_zero),8);
if(connect(sock,(struct sockaddr *)&server_addr,sizeof(struct sockaddr))==-1)



{

perror("Connect"); exit(1);
}

while(1)

{

bytes_received=recv(sock,receive,20,0); receive[bytes_received]='\0'; if(strcmp(receive,"exit")==0||strcmp(receive,"exit")==0)
{

close(sock); break;
}

else

{

if(strlen(receive)<10)

{

printf("\n Frame %d data %s received\n",i,receive); send(0,receive,strlen(receive),0);
}

else

{

send(0,"negative",10,0);

} i++;



}

}

close(sock); return(0);
}


















OUTPUT SENDER
$ cc sender.c

$ ./a.out

Enter Data Frame 1:(Enter exit for End): saveetha Enter Data Frame 2:(Enter exit for End): mca Enter Data Frame 3:(Enter exit for End): exit
$



RECEIVER

$ cc receiver.c



$ ./a.out Socket created
Frame 1 data saveetha received Frame 2 data mca received
$




HOST INFORMATION


#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <errno.h>
#include <netdb.h>
#include <arpa/inet.h>

int get_ip(char *  , char *);

int main(int argc , char *argv[])
{if(argc <2)
    {printf("Please provide a hostname");
      exit(1);}
    char *hostname = argv[1];
    char ip[100];
    get_ip(hostname , ip);
    printf("%s resolved to %s" , hostname , ip);
    printf("\n");}

int get_ip(char * hostname , char* ip)
{  struct hostent *he;
   struct in_addr **addr_list;
   int i;
   if ( (he = gethostbyname( hostname ) ) == NULL)
   { herror("gethostbyname");
     return 1;}
   addr_list = (struct in_addr **) he->h_addr_list;
    for(i = 0; addr_list[i] != NULL; i++)
    {   strcpy(ip , inet_ntoa(*addr_list[i]) );
        return 0;}
    return 1;
}




DAY TIME SERVER

#include<netinet/in.h>
#include<sys/socket.h>
main( )
{
struct sockaddr_in sa;
struct sockaddr_in cli;
int sockfd,coontfd;
int len,ch;
char str[100];
time_t tick;
sockfd=socket(AF_INET,SOCK_STREAM,0);
if(socket<0)
{
printf(“error in socket\n”);
exit(0);
}
else
printf(“Socket Opened”);
bzero(7sa,sizeof(sa));
sa.sin_port=htons(5600);
sa.sin_addr.s_addr=htonl(0);
if(bind(sockfd,(struct sockaddr*)&sa,sizeof(sa))<0)
{
printf(“Error in binding\n”);
}
else
printf(“Binded Successfully”);
listen(sockfd,50)
for(;;)
{
len=sizeof(ch);
conntfd=accept(sockfd,(struct sockaddr*)&cli,&len);
printf(“Accepted”);
tick=ctime(NULL);
snprintf(str,sizeof(str),”%s”,ctime(&tick));
write(conntfd,str,100);
}
}



DAY TIME CLIENT

#include<netinet/in.h>
#include<sys/socket.h>
main()
{
struct sockaddr_in sa,cli;
int n,sockfd;
int len;
char buff[100];
sockfd=socket(AF_INET,SOCK_STREAM,0);
if(sockfd<0)
{
printf(“Error in Socket”);
exit(0);
}
else
printf(“Socket is Opened”);
bzero(&sa,sizeof(sa));
sa.sin_family=AF_INET;
sa.sin_port=htons(5600);
if(connect(sockfd,(struct sockaddr*)&sa,sizeof(sa))<0)
{
printf(“Error in connection failed”);
exit(0);
}
else
printf(“connected successfully”):
if(n=read(sockfd,buff,sizeof(buff))<0)
{
printf(“Error in Reading”);
exit(0);
}
else
{
printf(“Message Read %s”,buff);
buff[n]=’\0’;
printf(“%s”,buff);
}
}





Chat App TCP IP - client


#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/socket.h>
#include<netdb.h>
#include<arpa/inet.h>

void error(char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc,char* argv[])
{
    int sockfd,portno;
    char recvbuffer[256],sendbuffer[256];
    struct sockaddr_in ser_addr;
    struct hostent* server;
    int i;

    if(argc<3)
    error("./client hostname portno");

    server=gethostbyname(argv[1]);
    portno=atoi(argv[2]);

    bzero((char*)&ser_addr,sizeof(ser_addr));
    ser_addr.sin_family=AF_INET;
    bcopy((char*)server->h_addr,(char*)&ser_addr.sin_addr.s_addr,server->h_length);
    ser_addr.sin_port=htons(portno);

    sockfd=socket(AF_INET,SOCK_STREAM,0);
    if(sockfd==-1)
    error("error in socket descriptor");
    printf("\nsocket created\n");

    if(connect(sockfd,(struct sockaddr*)&ser_addr,sizeof(ser_addr))==-1)
    error("error in connect");
    printf("\nconnect  successfully\n");

    bzero(recvbuffer,sizeof(recvbuffer));
    bzero(sendbuffer,sizeof(sendbuffer));

    i=fork();
    if(i==0)
    {
        printf("\nfork reading\n");
        while(1)
        {
            if(read(sockfd,recvbuffer,sizeof(recvbuffer))<0)
            error("error in reading");
            printf("\nserver:%s\n",recvbuffer);
            bzero(recvbuffer,sizeof(recvbuffer));
        }
    }
    else
    {
        printf("\n fork writing\n");
        while(1)
        {
            scanf("%s",sendbuffer);
            if(write(sockfd,sendbuffer,sizeof(sendbuffer))<0)
            error("error in writing");
        }
    }
    close(sockfd);
    return 0;
}




Chat App TCP IP - Server



#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/socket.h>
#include<netdb.h>
#include<arpa/inet.h>

void error(char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc,char* argv[])
{
    int sockfd,newsockfd,portno;
    char recvbuffer[256],sendbuffer[256];
    struct sockaddr_in ser_addr,cli_addr;
    int i;

    if(argc<2)
    error("./server portno");

    portno=atoi(argv[1]);

    bzero((char*)&ser_addr,sizeof(ser_addr));
    ser_addr.sin_family=AF_INET;
    ser_addr.sin_addr.s_addr=INADDR_ANY;
    ser_addr.sin_port=htons(portno);

    sockfd=socket(AF_INET,SOCK_STREAM,0);
    if(sockfd==-1)
    error("error in socket descriptor");
    printf("\nsocket created\n");

    if(bind(sockfd,(struct sockaddr*)&ser_addr,sizeof(ser_addr))==-1)
    error("error in binding");
    printf("\nbinding successful\n");

    if(listen(sockfd,5)==-1)
    error("error in listening");
    printf("\nlisten successfully\n");

    bzero(recvbuffer,sizeof(recvbuffer));
    bzero(sendbuffer,sizeof(sendbuffer));


    newsockfd=accept(sockfd,(struct sockaddr*)NULL,NULL);

    i=fork();
    if(i==0)
    {
        printf("\nfork reading\n");
        while(1)
        {
            if(read(newsockfd,recvbuffer,sizeof(recvbuffer))<0)
            error("error in reading");
            printf("\nclient:%s\n",recvbuffer);
            bzero(recvbuffer,sizeof(recvbuffer));
        }
    }
    else
    {
        printf("\n fork writing\n");
        while(1)
        {
            scanf("%s",sendbuffer);
            if(write(newsockfd,sendbuffer,sizeof(sendbuffer))<0)
            error("error in writing");
        }

    }
    close(newsockfd);
    return 0;
}


File Transfer Client


#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/socket.h>
#include<netdb.h>
#include<arpa/inet.h>

void error(char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc,char* argv[])
{
    int sockfd,portno;
    char buffer[256];
    struct sockaddr_in ser_addr;
    struct hostent* server;

    if(argc<3)
    error("./client hostname portno");

    server=gethostbyname(argv[1]);
    portno=atoi(argv[2]);

    bzero((char*)&ser_addr,sizeof(ser_addr));
    ser_addr.sin_family=AF_INET;
    bcopy((char*)server->h_addr,(char*)&ser_addr.sin_addr.s_addr,server->h_length);
    ser_addr.sin_port=htons(portno);

    sockfd=socket(AF_INET,SOCK_STREAM,0);
    if(sockfd==-1)
    error("error in socket descriptor");
    printf("\nsocket created\n");

    if(connect(sockfd,(struct sockaddr*)&ser_addr,sizeof(ser_addr))==-1)
    error("error in connect");
    printf("\nconnect  successfully\n");

    FILE* fp;
    int nread;
    fp=fopen("sample1.txt","r");
    if(fp==NULL)
    error("error in file opening");

    while(1)
    {
        nread=fread(buffer,1,sizeof(buffer),fp);
        if(nread>0)
        write(sockfd,buffer,nread);
        if(nread<256)
        {
            if(feof(fp))
            printf("\nEnd of file\n");

            if(ferror(fp))
            printf("\n error in file\n");

            break;
        }
    }
    close(sockfd);
    return 0;
}


File Transfer Server




#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/socket.h>
#include<netdb.h>
#include<arpa/inet.h>

void error(char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc,char* argv[])
{
    int sockfd,newsockfd,portno;
    char buffer[256];
    struct sockaddr_in ser_addr;

    if(argc<2)
    error("./server portno");

    portno=atoi(argv[1]);

    bzero((char*)&ser_addr,sizeof(ser_addr));
    ser_addr.sin_family=AF_INET;
    ser_addr.sin_addr.s_addr=INADDR_ANY;
    ser_addr.sin_port=htons(portno);

    sockfd=socket(AF_INET,SOCK_STREAM,0);
    if(sockfd==-1)
    error("error in socket descriptor");
    printf("\nsocket created\n");

    if(bind(sockfd,(struct sockaddr*)&ser_addr,sizeof(ser_addr))==-1)
    error("error in binding");
    printf("\nbinding successful\n");

    if(listen(sockfd,5)==-1)
    error("error in listening");
    printf("\nlisten successfully\n");

    newsockfd=accept(sockfd,NULL,NULL);

    FILE* fp;
    int nread;
    fp=fopen("sample.txt","ab");
    if(fp==NULL)
    error("error in file opening");

    while((nread=read(newsockfd,buffer,sizeof(buffer)))>0)
    {
        fwrite(buffer,1,nread,fp);
        bzero(buffer,sizeof(buffer));
    }

    close(newsockfd);
    return 0;
}



Message Transfer Client UDP


#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/socket.h>
#include<netdb.h>
#include<arpa/inet.h>

void error(char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc,char* argv[])
{
    int sockfd,portno;
    char buffer[256];
    struct sockaddr_in ser_addr;
    struct hostent* server;

    if(argc<3)
    error("./client hostname portno");

    server=gethostbyname(argv[1]);
    portno=atoi(argv[2]);

    bzero((char*)&ser_addr,sizeof(ser_addr));
    ser_addr.sin_family=AF_INET;
    bcopy((char*)server->h_addr,(char*)&ser_addr.sin_addr.s_addr,server->h_length);
    ser_addr.sin_port=htons(portno);

    sockfd=socket(AF_INET,SOCK_STREAM,0);
    if(sockfd==-1)
    error("error in socket descriptor");
    printf("\nsocket created\n");

    if(connect(sockfd,(struct sockaddr*)&ser_addr,sizeof(ser_addr))==-1)
    error("error in connect");
    printf("\nconnect  successfully\n");

    bzero(buffer,sizeof(buffer));


    while(1)
    {
        printf("\nEnter message for server:");
        scanf("%s",buffer);
        if(write(sockfd,buffer,sizeof(buffer))<0)
        printf("writing error");

        if(read(sockfd,buffer,sizeof(buffer))<0)
        printf("\n message read error\n");

        printf("\nmessage got from client:%s",buffer);
        bzero(buffer,sizeof(buffer));


    }
    close(sockfd);
    return 0;
}




Username password server

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
int main(int argc, char *argv[])
{
int sock_des,port,n1,n2,s1,s2;
char null_character;
char buffer1[100],buffer2[100],buffer3[100],buffer4[100];
int length,new_des;
struct sockaddr_in server_addr,client_addr;
bzero(buffer3,sizeof(buffer3));
printf("\n Input Authentic Username :\n");
scanf("%s",buffer3);
bzero(buffer4,sizeof(buffer4));
printf("\n Input Authentic Password :\n");
scanf("%s",buffer4);
if(argc!=2)
{
printf("Usage: ./server port\n");
exit(1);
}
port= atoi(argv[1]);
if((sock_des=socket(AF_INET,SOCK_STREAM,0))==-1)
{
perror("socket");
exit(1);
}


server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(port);
server_addr.sin_addr.s_addr= htonl(INADDR_ANY);
if (bind(sock_des,(const struct sockaddr *)&server_addr,sizeof(struct sockaddr))==-1)
{
perror("bind");
exit(1);
}
if( listen(sock_des,5)==-1)
{
perror("listen");
exit(1);
}
printf("Server is listening at port %d \n", port);
while(1)
{
if((new_des=accept(sock_des,(struct sockaddr *)&client_addr,&length))==-1)
{
perror("accept");
exit(1);
}
bzero(buffer1,sizeof(buffer1));
n1=read(new_des,buffer1,sizeof(buffer1));
buffer1[n1]=null_character;
if((s1=strcmp(buffer1,buffer3))==0)
{
write(new_des,"Username Match!Enter Password",30);
printf("Username Match !!!\n");
bzero(buffer2,sizeof(buffer2));
n2=read(new_des,buffer2,sizeof(buffer2));
buffer2[n2]=null_character;
if((s2=strcmp(buffer2,buffer4))==0)
{
write(new_des,"Password Match",15);
printf("Password Match !!!\n");
}
else
{
write(new_des,"Password NOT Match",19);
printf("Password NOT Match !!!\n");
}
}
else
{
write(new_des,"Username Not Match",19);
printf("Username Not Match !!!\n");
}
close(new_des);
}
}


Username password Client

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
int main(int argc,char *argv[])
{
int sock_des,port,n;
char null_character;
struct hostent *host;
char buffer1[100],buffer2[100],buffer3[100],buffer4[100];
struct sockaddr_in server_addr;
if(argc!=3)
{
printf("Usage: ./client hostname port\n");
exit(1);
}
if((host=gethostbyname(argv[1]))==NULL)
{
printf("Unknown Host\n");
exit(1);
}
port = atoi(argv[2]);
if((sock_des=socket(AF_INET,SOCK_STREAM,0))==-1)
{
perror("socket");
exit(1);
}
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(port);
server_addr.sin_addr = *((struct in_addr *)host->h_addr);
if(connect(sock_des,(struct sockaddr *)&server_addr,sizeof(struct sockaddr))==-1)
{
perror("connect");
exit(1);
}
bzero(buffer1,sizeof(buffer1));
printf("Enter the Username :\n");
scanf("%s",buffer1);
write(sock_des,buffer1,sizeof(buffer1));
bzero(buffer4,sizeof(buffer4));


n=read(sock_des,buffer4,sizeof(buffer4));
buffer4[n]= null_character;
printf("Server Sent : %s\n", buffer4);
bzero(buffer2,sizeof(buffer2));
printf("Enter the Password :\n");
scanf("%s",buffer2);
write(sock_des,buffer2,sizeof(buffer2));
bzero(buffer3,sizeof(buffer3));
n=read(sock_des,buffer3,sizeof(buffer3));
buffer3[n]=null_character;
printf("Server Sent : %s\n", buffer3);
close(sock_des);
}






Message Transfer Server UDP



#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/socket.h>
#include<netdb.h>
#include<arpa/inet.h>

void error(char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc,char* argv[])
{
    int sockfd,newsockfd,portno;
    char buffer[256];
    struct sockaddr_in ser_addr;

    if(argc<2)
    error("./server portno");

    portno=atoi(argv[1]);

    bzero((char*)&ser_addr,sizeof(ser_addr));
    ser_addr.sin_family=AF_INET;
    ser_addr.sin_addr.s_addr=INADDR_ANY;
    ser_addr.sin_port=htons(portno);

    sockfd=socket(AF_INET,SOCK_STREAM,0);
    if(sockfd==-1)
    error("error in socket descriptor");
    printf("\nsocket created\n");

    if(bind(sockfd,(struct sockaddr*)&ser_addr,sizeof(ser_addr))==-1)
    error("error in binding");
    printf("\nbinding successful\n");

    if(listen(sockfd,5)==-1)
    error("error in listening");
    printf("\nlisten successfully\n");

    newsockfd=accept(sockfd,NULL,NULL);

    bzero(buffer,sizeof(buffer));

    while(1)
    {
        if(read(newsockfd,buffer,sizeof(buffer))<0)
        printf("\n message read error\n");

        printf("\nmessage got from client:%s",buffer);
        bzero(buffer,sizeof(buffer));

        printf("\nEnter message for client:");
        scanf("%s",buffer);
        if(write(newsockfd,buffer,sizeof(buffer))<0)
        printf("writing error");
    }
    close(newsockfd);
    return 0;
}





ECHO - UDP


#include <stdio.h>      /* standard C i/o facilities */
#include <stdlib.h>     /* needed for atoi() */
#include <unistd.h>     /* defines STDIN_FILENO, system calls,etc */
#include <sys/types.h>  /* system data type definitions */
#include <sys/socket.h> /* socket specific definitions */
#include <netinet/in.h> /* INET constants and stuff */
#include <arpa/inet.h>  /* IP address conversion stuff */
#include <netdb.h>      /* gethostbyname */



/* this routine echos any messages (UDP datagrams) received */

#define MAXBUF 1024*1024

void echo( int sd ) {
    int len,n;
    char bufin[MAXBUF];
    struct sockaddr_in remote;

    /* need to know how big address struct is, len must be set before the
       call to recvfrom!!! */

    len = sizeof(remote);

    while (1) {
      /* read a datagram from the socket (put result in bufin) */
      n=recvfrom(sd,bufin,MAXBUF,0,(struct sockaddr *)&remote,&len);

      /* print out the address of the sender */
      printf("Got a datagram from %s port %d\n",
             inet_ntoa(remote.sin_addr), ntohs(remote.sin_port));

      if (n<0) {
        perror("Error receiving data");
      } else {
        printf("GOT %d BYTES\n",n);
        /* Got something, just send it back */
        sendto(sd,bufin,n,0,(struct sockaddr *)&remote,len);
      }
    }
}

/* server main routine */

int main() {
  int ld;
  struct sockaddr_in skaddr;
  int length;

  /* create a socket
     IP protocol family (PF_INET)
     UDP protocol (SOCK_DGRAM)
  */

  if ((ld = socket( PF_INET, SOCK_DGRAM, 0 )) < 0) {
    printf("Problem creating socket\n");
    exit(1);
  }

  /* establish our address
     address family is AF_INET
     our IP address is INADDR_ANY (any of our IP addresses)
     the port number is assigned by the kernel
  */

  skaddr.sin_family = AF_INET;
  skaddr.sin_addr.s_addr = htonl(INADDR_ANY);
  skaddr.sin_port = htons(0);

  if (bind(ld, (struct sockaddr *) &skaddr, sizeof(skaddr))<0) {
    printf("Problem binding\n");
    exit(0);
  }

  /* find out what port we were assigned and print it out */

  length = sizeof( skaddr );
  if (getsockname(ld, (struct sockaddr *) &skaddr, &length)<0) {
    printf("Error getsockname\n");
    exit(1);
  }

  /* port number's are network byte order, we have to convert to
     host byte order before printing !
  */
  printf("The server UDP port number is %d\n",ntohs(skaddr.sin_port));

  /* Go echo every datagram we get */
  echo(ld);
  return(0);
}




list all ports hosting a TCP server in a specified host.


#include(stdio.h)

#include(arpa/inet.h)

#include(netdb.h)

#include(stdlib.h)

int main(int argc,char* argv[])

{

struct hostent *host;

struct sockaddr_in server_addr;

int sock_des,port;

if(argc != 2)

{

printf(“Usage ;./a.out hostname \n”);

exit(1);

}

if ((host=gethostbyname(argv[1])) == NULL)

{

printf(“Unknown Host\n”);

exit(1);

}

for(port = 0; port<= 65535; port++)

{

if((sock_des = socket(AF_INET,SOCK_STREAM,0) == -1))

{

perror(“socket”);

exit(1);

}

server_addr.sin_family = AF_INET;

server_addr.sin_port = htons(port);

server_addr.sin_addr = *((struct in_addr *)host->h_addr);

if (connect(sock_des, (struct sockaddr *)&server_addr, sizeof(struct sockaddr))

!= -1)

{

printf(“port %d is open \n”,port);

}

close(sock_des);

}

return 0 ;

}


****EOF****
Checksum
#include<stdio.h>
#include<conio.h>
#include<math.h>

 int sender(int b[10],int k)
 {
 	int checksum,sum=0,i;
        	printf("\n****SENDER****\n");

for(i=0;i<k;i++)
      		sum+=b[i];
      		printf("SUM IS: %d",sum);

    	checksum=~sum;
    	printf("\nSENDER's CHECKSUM IS:%d",checksum);
    	return checksum;
}

int receiver(int c[10],int k,int scheck)
{
int checksum,sum=0,i;
     	printf("\n\n****RECEIVER****\n");
     	for(i=0;i<k;i++)
      		sum+=c[i];
      	printf(" RECEIVER SUM IS:%d",sum);
      	sum=sum+scheck;
      	checksum=~sum;
      	printf("\nRECEIVER's CHECKSUM IS:%d",checksum);
      		return checksum;
  }
   main()
   {
     	int a[10],i,m,scheck,rcheck;
clrscr();
     	printf("\nENTER SIZE OF THE STRING:");
     	scanf("%d",&m);
     	printf("\nENTER THE ELEMENTS OF THE ARRAY:");
     	for(i=0;i<m;i++)
    	scanf("%d",&a[i]);
    	scheck=sender(a,m);
    	rcheck=receiver(a,m,scheck);
    	if(rcheck==0)
      		printf("\n\nNO ERROR IN TRANSMISSION\n\n");
    	else
      		printf("\n\nERROR DETECTED");
               getch();
}