In this shot, we will learn how to use the **`ratio_subtract()` function**. This template alias is used to subtract two ratios.

> The `ratio_subtract()` function is available in the `<ratio>` header file in C++.


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## 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_subtract()` function on these two ratios gives -13 : 6. Let’s explore how the addition took place.

* First, we need to find the #key# LCM: Lowest Common Multiple #key# of the denominators of the two fractions which will be the denominator of the subtraction.

* The LCM of 3 and 2 is 6.

* Now subtraction = $\frac{(1*2-5*3)}{6}$ = $\frac{-13}{6}$.

## Parameters
The `ratio_subtract()` 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 the subtraction in the simplest form.
It returns two member constants:
* `num`: The simplified numerator of the ratio after the subtraction of the two ratios.
* `den`: The simplified denominator of the ratio after the subtraction of the two ratios.

## Code
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_subtract< ratio1, ratio2 > diff;
    
  cout << "The ratio after addition is : ";
  cout << diff::num << "/" << diff::den;
  
  return 0;
}

## Explanation
* In lines 1 and 2, we import the required header files.
* In line 5, we make a `main()` function.
* From lines 7 and 8, we declare two ratios.
* In line 10, we perform the subtraction of the two declared ratios by using the `ratio_subtract()` function.
* In line 12, we display a message regarding the result.

* In line 13, we display the numerator and denominator by accessing them through the sum variable and display the result.


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



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

What is a ratio?

Parameters

Return value

Code

Explanation