Caesar Cipher in C (Encryption & Decryption)

Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plain text is replaced by a letter some fixed number of positions down the alphabet.

C Program:

	#include <stdio.h>
	#include <string.h> // for strlen() function
	#include <ctype.h> // for isupper() function
	void encrypt(char text[], int s)
	{
	int i;
	for (i=0; i<strlen(text); i++)
	{
	if (isupper(text[i]))
	text[i]= (text[i]+s-65)%26 +65;
	else
	text[i]= (text[i]+s-97)%26 +97;
	}
	}
	void dencrypt(char text[], int s)
	{
	int i;
	for (i=0; i<strlen(text); i++)
	{
	if (isupper(text[i]))
	text[i]= 65+ ((text[i]-s-65)%26+26)%26;
	else
	text[i]= 97+ ((text[i]-s-97)%26+26)%26;
	}
	}
	int main()
	{
	char text[100];
	int s,i;
	printf("Enter String: ");
	scanf("%s",&text);
	printf("Enter Key: ");
	scanf("%d",&s);
	printf("1.Encryption\n2.Decryption\nEnter choice: ");
	scanf("%d",&i);
	switch(i)
	{
	case 1:
	encrypt(text, s);
	printf("Cipher Text: %s",text);
	break;
	case 2:
	dencrypt(text, s);
	printf("Plain Text: %s",text);
	break;
	default:
	printf("Invalid input");
	break;
	}
	return 0;
	}

view raw Caesar.c hosted with ❤ by GitHub

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