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How to use the ratio_add() function in C++

Harsh Jain

In this shot, we will learn how to use the ratio_add() function. This template alias is used to add the two ratios.

The ratio_add() function is available in <ratio> header file in C++.

What is a ratio?

A ratio is a representation of a fraction in which the numerator and denominator are differentiated by a colon (:) symbol. The numerator and denominator can be of float data type.

Let’s understand with the help of an example. Suppose that the first ratio is 1 : 3 and the second ratio is 5 : 2. So, the result of the ratio_add() function on these two ratios gives the result as 17 : 6. Let’s dive into how the addition took place.

  • First, we need to find the LCMLowest Common Multiple of the denominators of the two fractions which will be the denominator of the addition.

  • The LCM of 3 and 2 is 6.

  • Now addition = (12+53)6\frac{(1*2+5*3)}{6} = 176\frac{17}{6}


The ratio_add() method takes the following parameters:

  • Ratio1: A ratio object for addition.
  • Ratio2: Another ratio object to perform the addition with the first ratio object.

Return value

This function returns the result of addition in the simplest form. It returns two member constants:

  • num: The simplified numerator of the ratio after the addition of the two ratios.
  • den: The simplified denominator of the ratio after the addition of the two ratios.


Let’s have a look at the code.

#include <iostream>
#include <ratio>
using namespace std;

int main()
  typedef ratio<1, 3> ratio1;
  typedef ratio<5, 2> ratio2;

  typedef ratio_add< ratio1, ratio2 > sum;
  cout << "The ratio after addition is : ";
  cout << sum::num << "/" << sum::den;
  return 0;
Use ratio_add() function in C++


  • In lines 1 and 2 we imported the required header files.

  • In line 5 we made a main() function.

  • From lines 7 and 8 we declared two ratios.

  • In line 10 we performed the sum of the two declared ratios by using ratio_add() function.

  • In line 12 we displayed a message regarding the result.

  • In line 13 we displayed the numerator and denominator by accessing them through the sum variable and displayed the result.

In this way, we can use the ratio_add() function to add two ratios and get the addition in the simplest form.



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