Write a program to implement ceaser cipher. GTU

/*PROGRAM TO IMPLEMENT CEASER CIPHER*/
#include<stdio.h>
main()
{
    FILE *fp;
    char a[100];
    int c,i,x;
    fp=fopen("TEXT.txt","r");
    fscanf(fp,"%[^\n]s",a);
    printf("INPUT STRING IS %s \n \n",a);
    printf("ENTER YOUR CHOICE 1-ENCRYPTION 2-DECRYPTION : ");
    scanf("%d",&x);
    if(x==1)
    {
        printf("ENTER THE ENCRYPTION KEY : ");
        scanf("%d",&c);
        while(c>26)
        {
            c=c-26;
        }
        for(i=0;a[i]!='\0';i++)
        {

            if(a[i]>=96 && a[i]<=122)
            {
                while((a[i]+c)>'z')
                {
                    a[i]=a[i]-26;
                }
                a[i]=((a[i]+c));
            }
            else if(a[i]>=65 && a[i]<=90)
            {
                while((a[i]+c)>'Z')
                {
                    a[i]=a[i]-26;
                }
                a[i]=((a[i]+c));
            }
            else if(a[i]==' ')
            {
                a[i]=' ';
            }
        }
        printf("ENCRPTED STRING IS : %s",a);
    }
    else if(x==2)
    {
        printf("ENTER THE DECRYPTION KEY : ");
        scanf("%d",&c);
        while(c>26)
        {
            c=c-26;
        }
        for(i=0;a[i]!='\0';i++)
        {

            if(a[i]>=96 && a[i]<=122)
            {
                while((a[i]-c)<'a')
                {
                    a[i]=a[i]+26;
                }
                a[i]=((a[i]-c));
            }
            else if(a[i]>=65 && a[i]<=90)
            {
                while((a[i]-c)<'A')
                {
                    a[i]=a[i]+26;
                }
                a[i]=((a[i]-c));
            }
            else if(a[i]==' ')
            {
                a[i]=' ';
            }
        }
        printf("DECYPRTED STRING IS : %s",a);
        }
}