这题直接用printf里面的%.2f就行，代码如下~

#include <bits/stdc++.h>
using namespace std;
int main()
{
    double x, y, temp = 0;
    cin >> x >> y;
    temp = x * y;
    printf ("%.2f",temp);
    return 0;
}

/*********************************
备注:
*********************************/
#include <iostream>
#include <cstdio>
#include <iomanip>
#include <cmath>
#include <math.h>
#include <algorithm>
#include <cstring>
#include <string>
#include <stack>
#include <queue>
#include <algorithm>
#define LL long long
using namespace std;
const int INF = 0x3f3f3f3f;
const int N = 1e5 + 10;
double n , m;
int main()
{
	cin >> n >> m;
	double zzz = n * m;
	cout << fixed << setprecision(2) << zzz << endl;
	return 0;
}

#include <iostream>
using namespace std;
int main(){
    double a,b;
    scanf("%lf%lf",&a,&b);
    printf("%.2lf",a*b);
    return 0;
}

 #include <bits/stdc++.h>

using namespace std;

int main(void)
{
	float x, y;

	cin >> x >> y;

	printf("%.2f", x * y);

	return 0;
}

#include <stdio.h>
#include <iostream>
using namespace std;
int main()
{
	double x,y;
	cin >> x >> y;
	printf("%.2lf",x*y);
}

#include<stdio.h> #include<iostream> using namespace std; int main() { double x,y; cin >> x >> y; printf("%.2lf,x*y);

return 0;

}

#include <stdio.h> #include <iostream> using namespace std; int main() { double x,y; cin >> x >> y; printf("%.2lf",x * y); }

#include<stdio.h> #include<iostream> #include<iomanip> using namespace std; int main() { double x,y; cin>>x>>y; cout<<fixed<<setprecision(2)<<x*y<<endl; }

#include <iostream>
#include <iomanip>
using namespace std;
int main(){
    double x,y;
    cin>>x>>y;
    cout<<fixed<<setprecision(2)<<x*y<<endl;
    return 0;
}