$AC$ 了，请各位大佬看看有没有错

#include<bits/stdc++.h>
using namespace std;
int main(){
    double money , part , month;
    cin >> money >> part >> month;
    double ans = 0 , mid , l , r = 400;
    while(l < r - 0.0001){
        mid = (l + r) / 2.0;
        double moni = money;
        for(int i = 1 ; i <= month ; i++){
            moni = moni - part + (moni) * (mid / 100);
        }
        if(moni > 0.0001){
            r = mid;
        }
        else{
            l = mid;
        }
    }
    printf("%.1lf" , mid);
    return 0;
}

再问一句 在c++中咋写四舍五入？