- ceil 向上取整
- round 四舍五入取整
#include <iostream>
#include <math.h>
using namespace std;
int main(){
double C1,C2;
cin >> C1 >> C2;
int h=0,min=0;
int sum=int (round((C2-C1)/100));
h = sum/3600;
sum-=h*3600;min = sum/60;sum-=min*60;
printf("%02d:%02d:%02d",h,min,sum);
}