题解 | 添加逗号

#include <stdio.h>

int main() {
	char num[20] = { " " };
	int i = 0;
	char num1[20] = { " " };
	int times = 0;
	for (i = 0; scanf("%c", &num[i]) != EOF; i++) {
	}
	i -= 1;
	for (int j = 0; i > 0; j++) {
		if (times == 3) {
			times = 0;
			num1[j] = ',';
			j++;
		}
		times++;
		i--;
		num1[j] = num[i];
	}
	for (int j = 19; j >= 0; j--) {
		if (num1[j] != '\0') {
			printf("%c", num1[j]);
		}
	}
	return 0;
}