Calculator 1

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <stdbool.h>

bool valid (int argc, char* argv[]) {
    if (argc == 4) {
        if (strtod(argv[1], NULL) != 0 && strtod(argv[3], NULL) != 0) {
            if (strcmp(argv[2], "+") == 0 || strcmp(argv[2], "x") == 0 || strcmp(argv[2], "/") == 0 || strcmp(argv[2], "-") == 0) {
                return true;
            } else {
                fprintf(stderr, "Invalid operation!\n");
            }
        } else {
            fprintf(stderr, "Arguments are not numbers!\n");
        }
    } else {
        fprintf(stderr, "Invalid argument count!\n");
    }

    return false;
}

int main (int argc, char* argv[]) {
    double num1, num2;
    double result = 0.0;


    if (valid(argc, argv)) {
        num1 = strtod(argv[1], NULL);
        num2 = strtod(argv[3], NULL);

        if (strcmp(argv[2], "+") == 0) {
            result = num1 + num2;
        } else if (strcmp(argv[2], "x") == 0) {
            result = num1 * num2;
        } else if (strcmp(argv[2], "/") == 0) {
            result = num1 / num2;
        } else if (strcmp(argv[2], "-") == 0) {
            result = num1 - num2;
        }
    } else {
        return 1;
    }

    printf("Result = %.2f\n", result);

    return 0;
}