#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);
}