#include <stdio.h>
#include <string.h>
int checkemail(char email[], int stringlength);
int main ()
{
    char email[]="";
    int stringlength;

    printf("Enter an email address: ");
    scanf("%s", email);

    stringlength=strlen(email);

    if (checkemail(email,stringlength)==1)
       printf("\nThis string is a valid email address!\n");
    else
       printf("\nThis string is not a valid email address.\n");

    system("PAUSE");
    return 0;
}

int checkemail(char email[], int stringlength)
 {
   int sum=0;
   int i, atindexrecorder, temp;

   for(i=0;i<=stringlength;i++)
    if(email[i]=='@')
     {
     atindexrecorder=i;
     sum++;
     }

   if (sum==1)
    {
     printf("Filter 1: OK\n");

     if(email[0]!='@' && email[stringlength-1]!='@')
       {
         printf("Filter 2: OK\n");
         sum++;
       }
     else
       printf("Filter 2: FAIL\n");

       temp=sum;

     for(i=atindexrecorder;i<=stringlength;i++)
       if(email[i]=='.')
        {
         sum++;
         printf("Filter 3: OK\n");
         break;
        }
       if(temp==sum)
         printf("Filter 3: Fail\n");

     if (email[atindexrecorder-1]!='.' && email[atindexrecorder+1]!='.')
       {
         sum++;
         printf("Filter 4: OK\n");
       }
     else
         printf("Filter 4: Fail\n");
    }


   else
    {
      sum==0;
      printf("Filter 1: Fail\nFilter 2: Fail\nFilter 3: Fail\nFilter 4: Fail\n");
    }
   temp=0;

   for(i=0;i<=stringlength-1;i++)
    if(!( (email[i]>='@' && email[i]<='Z') || (email[i]>='a' && email[i]<='z')
       || (email[i]>='0' && email[i]<='9') || email[i]=='.' || email[i]=='-'
       || email[i]=='_'))
          temp++;
    if(temp==0)
     {
      sum++;
      printf("Filter 5: OK\n");
     }
    else
      printf("Filter 5: Fail\n");

   if(email[0]!='.' && email[stringlength-1]!='.')
    {
      sum++;
      printf("Filter 6: OK\n");
    }
    else
      printf("Filter 6: Fail\n");

   temp=0;
   for(i=0;i<=stringlength-1;i++)
     if(email[i]=='.')
       if(email[i+1]=='.')
         temp++;
   if (temp==0)
    {
      sum++;
      printf("Filter 7: OK\n");
    }
   else
       printf("Filter 7: Fail\n");

   if(sum==7)
    return 1;
   else
    return 0;

 }