题解 | #添加逗号#

#include <stdio.h>
#include <math.h>
int main() {
    int a;
    scanf("%d", &a);
    int i = a, count = 0;
    while (i / 10) {
        count++;
        i /= 10;
    }
    if (a > 999) {
        while (count) {
            while (count % 3 != 0)
                count--;
            printf("%d,", a / (int)pow(10, count));
            a %= (int)pow(10, count);
            count -= 3;
        }
        printf("%03d", a);
    } else {
        printf("%d", a);
    }
    return 0;
}