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

Harsh Jain

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++.

### 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 LCMLowest Common Multiple 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;
}
Use ratio_subtract() function in C++

### 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.

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