NIS Lab1

//Caeser Cipher

#include<stdio.h>

char* encrypt(char* PT, int key);
char* decrypt(char* CT, int key);


int main()
{
    char text[26]="abcdefghijklmnopqrstuvwxyz";
    char PT[50], CT[50];
    int key;
    printf("\nEnter PT: ");
    scanf("%s",&PT);

    printf("\nEnter Key: ");
    scanf("%d",&key);

    printf("%s",encrypt(PT,key));



    printf("\nEnter CT: ");
    scanf("%s",&CT);

    printf("\nEnter Key: ");
    scanf("%d",&key);

    printf("%s",decrypt(CT,key));
    int i;

    printf("\nEnter CT: ");
    scanf("%s",&CT);

    for(i=0;i<26;i++)
    {
        printf("%d - %s\n",i,decrypt(CT,i));

    }

    return 0;
}

char* encrypt(char* PT, int key)
{
    char text[26]="abcdefghijklmnopqrstuvwxyz";
    char CT[50];

    int i,j,k;

    for(i=0;PT[i]!='\0';i++)
    {
        for(j=0;j<26;j++)
        {
            if(PT[i]==text[j])
            {
                break;
            }
        }
        k=((j+key)%26);
        CT[i]=text[k];
    }
    CT[i] = '\0';
    return CT;
}


char* decrypt(char* CT, int key)
{
    char text[26]="abcdefghijklmnopqrstuvwxyz";
    char PT[50];

    int i,j,k,l;

    for(i=0;CT[i] != '\0';i++)
    {
        for(j=0;j<26;j++)
        {
            if(CT[i]==text[j])
            {
                break;
            }
        }
        k=(j-key);
        if(k<0)
        {
            k +=26;

        }
        l=k%26;
        PT[i]=text[l];
    }
    PT[i] = '\0';
    return PT;
}