How do I print integer values without additional zeroes after comma by using cout in C++?

Question

Basically my code is about calculating equilateral triangle perimeter. Given values are these:

3
2.5 3 5.15

First number defines how many triangles there are and the numbers in second line are each triangle's side length.

Here's my code:

#include <iostream>
#include <fstream>
#include <cmath>
#include <iomanip>
#include <algorithm>
#include <cstdlib>+
using namespace std;

double Strik(double a);
int main()
{
    int n;
    cin>>n;
    double arr[n];
    for(int i=0;i<n;i++){
        cin>>arr[i];
    }
        for(int i=0;i<n;i++){
        cout<<fixed<<setprecision(2)<<arr[i]<<" "<<Strik(arr[i])<<endl;
    }
    return 0;
}
double Strik(double a){
double s  = ((a*a)*sqrt(3))/4;
 return s;
 }

Cout needs to be like this:

2.5 2.71
3 3.90
5.15 11.48

But I get this:

2.5 2.71
3.00 3.90
5.15 11.48

Please help

Answer 1

std::setprecision specifies the maximum number of digits to use and if you want to get N digits all the time you need to use std::fixed.

#include <iostream>
#include <iomanip>

int main()
{
    double a = 3.5;
    std::cout << std::fixed;
    std::cout << std::setprecision(4);
    std::cout << a << "\n";
    return 0;
}

And now the output is 3.5000.

Opposite from std::fixed is std::defaultfloat and in the first column you need std::defaultfloat but in the second column you need std::fixed so this is the way to go for you:

cout << defaultfloat << setprecision(2) << arr[i] << " ";
cout << fixed << Strik(arr[i]) << endl;

Check out live

UPDATE

If, as said in one of the comments, you want to output number 13.6, then you need to increase precision like this:

cout << defaultfloat << setprecision(3) << arr[i] << " ";
cout << fixed << setprecision(2) << Strik(arr[i]) << endl;