Sample code for An ASCII Encryption and Decryption code in C-language only.

#include<stdio.h>

void main(){
    FILE *fp1,*fp2;
    int choice;
    char fname[20],temp[20]={"file.txt"},c;
    clrscr();
    printf("Press 1 to Encrypt");
    printf("Press 2 to Decrypt");
    printf("Enter your Choice:");
    scanf("%d",&choice);

    switch(choice){
    case 1:
    printf("Enter the filename to Encrypt:");
    scanf("%s",fname);
    fp1=fopen(fname,"r+");
    if(fp1==NULL) {
         printf("The file %s can't be open",fname);
         getch();
         exit();
    }
    fp2=fopen(temp,"w+");
    if(fp2==NULL){
         printf("The file Temp can't be open");
         getch();
         exit();
    }
    c=fgetc(fp1);
    while(c!=EOF){
         fputc((c+fname[0]),fp2);
         printf("%c",c+fname[0]);
         getch();
         c=fgetc(fp1);
    }
     fclose(fp1);
     fclose(fp2);
     remove(fname);
     rename(temp,fname);
     printf("The file is Encrypted:");
     getch();
     break;

     case 2:
     printf("Enter the Filename to Decrypt:");
     scanf("%s",fname);
     fp1=fopen(fname,"r+");
     fp2=fopen(temp,"w+");
     c=fgetc(fp1);
     while(c!=EOF){
         fputc(c-fname[0],fp2);
         c=fgetc(fp1);
     }
     fclose(fp1);
     fclose(fp2);
     remove(fname);
     rename(temp,fname);
     printf("The file is decrypted:");
     getch();
  }
}