#include <stdio.h>
#define MAXSTRINGSIZE 140

int main (void) {
	char OriginalMessage[MAXSTRINGSIZE];
	char EncryptedMessage[MAXSTRINGSIZE];
	char ch = 0;
	int ch_count = 0;
	int i;
	int Letter;

	printf("Enter a message of 140 characters or less to be encrypted: ");
	while (ch != '\n') {
		ch = getchar();
		OriginalMessage[ch_count] = ch;
		ch_count++;
	}
	OriginalMessage[--ch_count] = 0;

	for (i = 0; i < ch_count; i++) {
		Letter = OriginalMessage[i];
		if (Letter >= 'A' && Letter <= 'M') {
			Letter += 13;
		}
		else if (Letter >= 'N' && Letter <= 'Z') {
			Letter -= 13;
		}
		else if (Letter >= 'a' && Letter <= 'm') {
			Letter += 13;
		}
		else if (Letter >= 'n' && Letter <= 'z') {
			Letter -= 13;
		}
		EncryptedMessage[i] = Letter;
	}
	EncryptedMessage[ch_count] = 0;

	printf("The encrypted message is: %s\n\n", EncryptedMessage);
}