题解 | 添加逗号

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
    char str[100];
    char str2[200];
    scanf("%s",str);
    int j = 0, count = 0;
    for(int i = strlen(str) - 1; i >= 0; i--){
        str2[j++] = str[i];
        count++;
        if(count % 3 == 0 && count && i != 0){
            str2[j++] = ',';
            count = 0;
        }
    }
    for(int i = j - 1; i>=0; i--)
        printf("%c",str2[i]);
    return 0;
}

复试2