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c++floating-pointprecisioniostream
thameera
thameera

Reputation: 9473

Printing the correct number of decimal places with cout

I have a list of float values and I want to print them with cout with 2 decimal places.

For example:

How can I do this?

(setprecision doesn't seem to help in this.)

Upvotes: 227

Views: 862625

Answers (13)

vitaut
vitaut

Reputation: 55524

In C++20 you can use std::format to do this:

std::cout << std::format("{:.2f}", 10.900);

Output:

10.90

It is less verbose and more efficient than using I/O manipulators. It also gives you control over locale with the default being locale-independent.

Disclaimer: I'm the author of C++20 std::format.

Upvotes: 6

Raihan Hossain
Raihan Hossain

Reputation: 169

Easiest way:

#include<stdio.h> 
int main() {
double d = 122.345;
printf(".2%lf",d); 
}

Upvotes: -1

Ryuzaki Lawliet
Ryuzaki Lawliet

Reputation: 61

#include <iostream>
#include <cstdio>
#include <iomanip>
using namespace std;

int main() {
    int a;
    long int b;
    char c;
    float d;
    double e;
    cin>>a>>b>>c>>d>>e;
    cout<<a<<"\n"<<b<<"\n"<<c<<"\n";
    cout<<fixed<<setprecision(3)<<d<<"\n";
    cout<<fixed<<setprecision(9)<<e;
    return 0;
}

Simple code would help you surely!

Upvotes: 2

QuentinUK
QuentinUK

Reputation: 3077

with templates

#include <iostream>

// d = decimal places
template<int d> 
std::ostream& fixed(std::ostream& os){
    os.setf(std::ios_base::fixed, std::ios_base::floatfield); 
    os.precision(d); 
    return os; 
}

int main(){
    double d = 122.345;
    std::cout << fixed<2> << d;
}

similar for scientific as well, with a width option also (useful for columns)

// d = decimal places
template<int d> 
std::ostream& f(std::ostream &os){
    os.setf(std::ios_base::fixed, std::ios_base::floatfield); 
    os.precision(d); 
    return os; 
}

// w = width, d = decimal places
template<int w, int d> 
std::ostream& f(std::ostream &os){
    os.setf(std::ios_base::fixed, std::ios_base::floatfield); 
    os.precision(d); 
    os.width(w);
    return os; 
}

// d = decimal places
template<int d> 
std::ostream& e(std::ostream &os){
    os.setf(std::ios_base::scientific, std::ios_base::floatfield); 
    os.precision(d); 
    return os; 
}

// w = width, d = decimal places
template<int w, int d> 
std::ostream& e(std::ostream &os){
    os.setf(std::ios_base::scientific, std::ios_base::floatfield); 
    os.precision(d); 
    os.width(w);
    return os; 
}

int main(){
    double d = 122.345;
    std::cout << f<10,2> << d << '\n'
        << e<10,2> << d << '\n';
}

Upvotes: 2

Hargun Singh
Hargun Singh

Reputation: 576

I had this similar problem in a coding competition and this is how I handled it. Setting a precision of 2 to all double values

First adding the header to use setprecision

#include <iomanip>

Then adding the following code in our main

  double answer=5.9999;
  double answer2=5.0000;
  cout<<setprecision(2)<<fixed;
  cout <<answer << endl;
  cout <<answer2 << endl;

Output:

5.99
5.00

You need to use fixed for writing 5.00 thats why,your output won't come for 5.00.

A short reference video link I'm adding which is helpful

Upvotes: 8

saurav52
saurav52

Reputation: 109

#include<stdio.h>
int main()

{

 double d=15.6464545347;

printf("%0.2lf",d);

}

Upvotes: 9

Hamid Rouhani
Hamid Rouhani

Reputation: 2459

To set fixed 2 digits after the decimal point use these first:

cout.setf(ios::fixed);
cout.setf(ios::showpoint);
cout.precision(2);

Then print your double values.

This is an example:

#include <iostream>
using std::cout;
using std::ios;
using std::endl;

int main(int argc, char *argv[]) {
    cout.setf(ios::fixed);
    cout.setf(ios::showpoint);
    cout.precision(2);
    double d = 10.90;
    cout << d << endl;
    return 0;
}

Upvotes: 3

Luis Enrique Martinez
Luis Enrique Martinez

Reputation: 25

this an example using a matrix.

cout<<setprecision(4)<<fixed<<m[i][j]

Upvotes: -5

beduin
beduin

Reputation: 8253

With <iomanip>, you can use std::fixed and std::setprecision

Here is an example

#include <iostream>
#include <iomanip>

int main()
{
    double d = 122.345;

    std::cout << std::fixed;
    std::cout << std::setprecision(2);
    std::cout << d;
}

And you will get output 

122.34

Upvotes: 333

einverne
einverne

Reputation: 6682

Simplify the accepted answer

Simplified example:

#include <iostream>
#include <iomanip>

int main()
{
    double d = 122.345;
    std::cout << std::fixed << std::setprecision(2) << d;
}

And you will get output 

122.34

Reference:

Upvotes: 20

Eric Z
Eric Z

Reputation: 14505

You have to set the 'float mode' to fixed.

float num = 15.839;

// this will output 15.84
std::cout << std::fixed << "num = " << std::setprecision(2) << num << std::endl;

Upvotes: 1

Vusak
Vusak

Reputation: 1470

You were nearly there, need to use std::fixed as well, refer http://www.cplusplus.com/reference/iostream/manipulators/fixed/

#include <iostream>
#include <iomanip>

int main(int argc, char** argv)
{
    float testme[] = { 0.12345, 1.2345, 12.345, 123.45, 1234.5, 12345 };

    std::cout << std::setprecision(2) << std::fixed;

    for(int i = 0; i < 6; ++i)
    {
        std::cout << testme[i] << std::endl;
    }

    return 0;
}

outputs:

0.12
1.23
12.35
123.45
1234.50
12345.00

Upvotes: 64

QuantumMechanic
QuantumMechanic

Reputation: 13946

setprecision(n) applies to the entire number, not the fractional part. You need to use the fixed-point format to make it apply to the fractional part: setiosflags(ios::fixed)

Upvotes: 22

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