在c中检查给定数字是否为二进制

Question

#include <stdio.h>

void binarytodecimal(int n);


int main() {

    int num;
    printf("Input a binary number: ");
    scanf("%d", &num);

    int copy = num, temp = 0;

    while(copy != 0) {
        temp = copy%10;

        if((temp==0) || (temp==1)) {
            copy = copy/10;
            if(copy == 0) {
                printf("valid binary number.\n");
                break;
            }
        }
        else {
            printf("Not a valid binary number. Try again\n");
            main();
        }

    }

    return 0;
}

This code is working perfectly fine for non binary numbers and for binary number when I run it in first attempt, but when I trie to input a binary number in the second attempt, it interpreted binary number as non binary.

I am stuck at this step.

Output shows

Input a binary number: 122
Not a valid binary number. Try again
Input a binary number: 101
valid binary number.
Not a valid binary number. Try again
Input a binary number:

Answer 1

As said using main() for a recursive routine is not the best idea, you might aswell make a separate function to do the same thing without that pesky main() recursive call.

#include <stdio.h>

void check_binary(int *num) {
    int copy, temp = 0;
    printf("Input a binary number: ");
    scanf("%d", num);
    copy = *num;

    while (copy != 0) {
        temp = copy % 10;

        if ((temp == 0) || (temp == 1)) {
            copy = copy / 10;
            if (copy == 0)
            {
                printf("valid binary number.\n");
                break;
            }
        }
        else {
            printf("Not a valid binary number. Try again\n");
            check_binary(num);
            break;
        }
    }
}

int main() {
    int num; //variable will be saved for future use
    check_binary(&num);
    return 0;
}

Live sample