將十進制舍入到十分之一，但在C++中顯示百分之一

Question

我一直在做這個家庭作業一段時間，準備把我的頭髮拉出來。

我需要幫助四捨五入到十分之一的位置，同時仍然在百位顯示0，我似乎沒有做任何事情。 即2.47 = 2.50

#include "stdafx.h" 
#include <iostream> 
#include <iomanip> 
using namespace std; 

int main() 
{ 
float MPH; 
float seconds; 
const float MPH2MPS = (1609.00/3600.00); 
float a; 

cout << "  Acceleration calculator" << endl; 
cout << "" << endl; 

cout << "Please enter the velocity in miles per hour: "; 
cin >> MPH; 
cout << "" << endl; 

cout << "Please enter the time in secounds: "; 
cin >> seconds; 
cout << "" << endl; 
cout << "" << endl; 
cout << "" << endl; 

a = MPH2MPS * (MPH/seconds); 

cout << showpoint << fixed << setprecision(2); 
cout << "The acceleration required by a vehicle to reach" << endl; 
cout << "" << endl; 

cout << "a velocity of " << MPH << " miles per hour in " << seconds << " seconds" << endl; 
cout << "" << endl; 

cout << "is " << setprecision(1) << a << " meters per second" << endl; 
cout << "" << endl; 
cout << "" << endl; 

system("pause"); 
return 0; 

任何想法？

Answer 1

閱讀@ asterite的回答here：

cout << "is " << static_cast<double>(std::round(a * 10))/10 << " meters per second" << endl; 

注意的round功能只適用，如果你#include <cmath>

更新： 修改文件math.h與CMATH，感謝@ user4581301