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PROGRAM
  1. #include<stdio.h>
  2. #include<strings.h>
  3. char *encryption(char []);
  4. void *decryption9char []);
  5. void main()
  6. {
  7.    int i, key, choice. flag=0;
  8.    char msg[255];
  9.    char *c_text;
  10.    printf("Enter plain text :");
  11.    scanf("%d", &choice);
  12.    printf("\n Your plain text message is : %s",msg);
  13.    do{
  14.       printf("\npress 1 for encryption \npress 2 for decryption \npress '0' for exit\n")
  15.       scanf("%d",&choice);
  16.       switch(choice) {
  17.          case 1 :
  18.             c_