#include<iostream>
#include<iomanip>
using namespace std;
int st1,st2,sp1,sp2;
char x;
int main(){
    cin>>st1>>x>>st2;
    cin>>sp1>>x>>sp2;
    double k=(sp1-st1)*60+(sp2-st2);
    cout<<fixed<<setprecision(1)<<k*0.5;
}

注：f为冒号，m代表分，h代表时，算出差分钟数，乘360/12*60（0.5°）即可

AC代码！！！！！！！

#include <bits/stdc++.h>
using namespace std;
int main()
{
    char f;
    int m1,m2,h1,h2;
    cin >> h1 >> f >> m1 >> h2 >> f >> m2;
    double k = (h2 - h1) * 60 + m2 - m1;
    cout << fixed << setprecision(1) << k * 0.5;
}