Encrypt and decrypt text - C Function

C examples for Function:Utility Function

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Description

Encrypt and decrypt text

Demo Code

#include <stdio.h> 
#include <stdlib.h> 

void encrypt(char [], int); 
void decrypt(char [], int); 

int main()//  w  ww  .j av a2s.c om
{ 
   char myString[21] = {0}; 
   int iSelection = 0; 
   int iRand; 

   iRand = (rand() % 4) + 1; // random #, 1-4 
   
   while ( iSelection != 4 ) { 
      printf("1\tEncrypt Clear Text\n");  
      printf("2\tDecrypt Cipher Text\n"); 
      printf("3\tGenerate New Key\n"); 
      printf("4\tQuit\n"); 
      printf("\nSelect a Cryptography Option: "); 
      scanf("%d", &iSelection); 
      switch (iSelection) { 
      case 1: 
         printf("\nEnter one word as clear text to encrypt: "); 
         scanf("%s", myString); 
         encrypt(myString, iRand); 
         break; 
      case 2: 
         printf("\nEnter cipher text to decrypt: "); 
         scanf("%s", myString); 
         decrypt(myString, iRand); 
         break; 
      case 3: 
         iRand = (rand() % 4) + 1; // random #, 1-4 
         printf("\nNew Key Generated\n"); 
         break; 
      }
   }
}
void encrypt(char sMessage[], int random) 
{ 
   int x = 0; 
   //encrypt the message by shifting each characters ASCII value 
   while ( sMessage[x] ) { 
      sMessage[x] += random; 
      x++;  
   }
   x = 0; 
   printf("\nEncrypted Message is: "); 

   while ( sMessage[x] ) { 
     printf("%c", sMessage[x]); 
     x++; 
   }
}
 
void decrypt(char sMessage[], int random) { 
   int x = 0; 
   x = 0; 
   //decrypt the message by shifting each characters ASCII value 
   while ( sMessage[x] ) { 
      sMessage[x] = sMessage[x] - random; 
      x++; 
   }
   x = 0; 
   printf("\nDecrypted Message is: "); 

   while ( sMessage[x] ) { 
     printf("%c", sMessage[x]); 
     x++; 
   }
}

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