C++ Increment and decrement operators

C++ Increment and decrement operators:

Increment and decrement operators are most commonly used operators in most programming languages like C, C++, Java etc. These are defined by ++ for increment and — for decrement.

The increment operator adds 1 and the decrement operator subtracts 1.

There are two more ways to use these operators: prefix and postfix.

In this post, we will learn how to use these operators, and how prefix and postfix versions works.

Prefix and Postfix versions:

Both increment and decrement operators can be used as:

Pre-Increment (++e)
Pre-Decrement (—e)
Post-Increment (e++)
Post-Decrement (e—)

For pre-increment or pre-decrement, the value is first incremented or decremented by 1 and it returns a reference to the result.

For post-increment or post-decrement, it returns the value first and then it increments or decrements the value by 1.

Example of pre and post increment/decrement:

Let’s create an example for pre and post increment.

#include <iostream>

using namespace std;

int main()
{
    int firstVar = 1;
    int secondVar = 1;

    cout << "++firstVar: " << ++firstVar << endl;
    cout << "secondVar++: " << secondVar++ << endl;

    cout << "firstVar: " << firstVar << endl;
    cout << "secondVar: " << secondVar << endl;

    return 0;
}

Here,

firstVar and secondVar are integer variables and these are initialized as 1.
The first two statements are printing the values of firstVar and secondVar while doing pre and post increment.
The last two statements are printing the values after the increment is done for the variables.

If you run this program, it will print the below output:

++firstVar: 2
secondVar++: 1
firstVar: 2
secondVar: 2

As you can see, for pre-increment, it returns the incremented value and for post-increment, it returns the value at current state.

Once the increment is done, it prints the same values for both.

Example of pre and post decrement:

We can change the above program to use with pre and post decrement as well. For example:

#include <iostream>

using namespace std;

int main()
{
    int firstVar = 1;
    int secondVar = 1;

    cout << "--firstVar: " << --firstVar << endl;
    cout << "secondVar--: " << secondVar-- << endl;

    cout << "firstVar: " << firstVar << endl;
    cout << "secondVar: " << secondVar << endl;

    return 0;
}

Similar to the above example, it will print:

--firstVar: 0
secondVar--: 1
firstVar: 0
secondVar: 0

As you can see, for pre-decrement the return value is the final value, i.e. 0 and for post-decrement, the return value is the value at current state.

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Updated on 9 Oct 2021

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