caesar.c

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

void caeser(char* input, int shift){
    do {
        *input = *input - 'a';      // convert to 0-idx alphabet
        *input = *input + shift;    // shift
        *input = *input % 26;       // wraparound going past z
        *input = *input + 'a';      // shift back to ascii alphabet
    } while (*++input);
    return;
}

int main(int argc, char* argv[]) {
    if (argc < 3){
        return 1;
    }

    int shift = atoi(argv[1]);

    for (int i = 2; i < argc; i++){
        caeser(argv[i], shift);
        printf("%s ", argv[i]);
    }
    printf("\n");
    return 0;
}