CaesarCipher in C! Will probably only work on Linux/Unix, I used the -std=c99 compiler.

CaesarCipher.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
/*encypt.c*/

// Function prototypes
int CipherChar(char *s, int offset);
int CipherStr(char *s, int offset);

// Array of characters declared globally to avoid scope issues.
int alpha[26] = {'a','b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'}; 

int main() {

	char *input = malloc(100 * sizeof(char));
	char c;
	int count = 0;
	int offset = 16;

	printf("Please enter string to be encrypted >> ");
	while( (c = getchar()) != '\n' ) {
		input[count++] = tolower(c);
	}

	CipherStr(input, offset);
}


int CipherStr(char *message, int offset) {
		for(int i = 0; i < strlen(message); i++) {
		char cha = message[i];
		printf("%c", CipherChar(&cha, offset));
	}
	printf("\n");
}

int CipherChar(char *s, int offset) {
	int i;
	for(i = 0; i < 26; i++) {
		int total = i + offset;		
			
		if(*s == alpha[i]) {
			while(total > 25) {
				total = total -26;
			}

			return alpha[total];
		}	
	}

	if (*s != alpha[i]) {
		return *s;
	}
}