Rotational Cipher

// usage: rot.exe <#> <left/right> "<string>"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char *argv[]){
    char* input = argv[3]; // get input
    char* shift = argv[2]; // location of shift
    char* num = argv[1]; // #num input
    int shiftAmount = atoi(num);
    if(num == NULL || input == NULL || shift == NULL){
        printf("Invalid Usage!\n");
        exit(8);
    }
    int i; // iterator
    if((strcmp(shift, "left") == 0) || (strcmp(shift, "right") == 0)){
        if(strcmp(shift, "right") == 0){
            for(i = 0; i < strlen(input); i++){
                if(input[i] + shiftAmount <= 126)
                       input[i] = input[i] + shiftAmount;
                else
                       input[i] = input[i] + shiftAmount - 94;
            }
        }else{
            for(i = 0; i < strlen(input); i++){
                if(input[i] - shiftAmount >= 32)
                       input[i] = input[i] - shiftAmount;
                else
                       input[i] = input[i] - shiftAmount + 94;
            }
        }
    }else{
        printf("Invalid Direction of Shift!\n");
        exit(8);
    }
    puts(input);
    // free up mem
    free(&input);
    free(&shift);
    return 0;
}