Increment (++) and Decrement (–) Operator in C++

By Ranjeet V

This tutorial is about the increment (++) and decrement (–) operator in C++. The increment operator increments the value of a variable while the decrement operator decrements the value of a variable by 1. Let’s discuss these operators in detail.

Increment Operator (++) in C++

The increment operator adds 1 to the value of a variable. There are two types of increment operator:

• Pre-increment operator
• Post-increment operator

The syntax for the increment operators is as follows:

a++  //post-increment operator

++a  //pre-increment operator

Here a is a variable.

Pre-increment Operator

A pre-increment operator increments the value of a variable before using it in the given statement. See the given code for a better understanding.

#include <iostream> 
using namespace std; 

int main() 
{ 
  int a,b=1;
  a=b; 
  cout<<"Value of b before increment operation is "<<b<<"."<<endl; 
  cout<<"Value of a before increment operation is "<<a<<"."<<endl; 
 
  //incrementing b and assigning its value to a 
  a=++b; 
  //printing value of a and b
  cout<<"Value of a after increment operation is "<<a<<"."<<endl; 
  cout<<"Value of b after increment operation is "<<b<<"."<<endl; 
  return 0; 
}

Output:

Value of b before increment operation is 1. 
Value of a before increment operation is 1. 
Value of a after increment operation is 2. 
Value of b after increment operation is 2.

Post-increment Operator

A post-increment operator uses the current value of a variable in the given expression before incrementing it. See the example code.

#include <iostream>
using namespace std; 
int main() 
{
  //declaring variable a and b 
  int a,b; 
  b=2;
  a=b;
  cout<<"Value of a before increment operation is "<<a<<"."<<endl;
  cout<<"Value of b before increment operation is "<<b<<"."<<endl;
 
  //post incrementing b and assigning its value to a 
  a=b++;
  
  //printing a and b 
  cout<<"Value of a after increment operation is "<<a<<"."<<endl; 
  cout<<"Value of b after increment operation is "<<b<<"."<<endl; 
  return 0; 
}

Output:

Value of a before increment operation is 2.
Value of b before increment operation is 2.
Value of a after increment operation is 2.
Value of b after increment operation is 3.

In the above code, the value of variable b is first stored in variable a and then b is incremented.

Decrement Operator (–) in C++

The decrement operator subtracts 1 from the value of a variable. There are two types of decrement operator:

• Pre-decrement operator
• Post-decrement operator

The syntax for the decrement operators is  given here:

a–  //post-decrement operator

–a // pre-decrement operator

Here a is a variable.

Pre-decrement Operator

A pre-decrement operator decrements the value of a variable before using it in the given statement. See the example code.

#include <iostream>
using namespace std;

int main()
{
  int a,i=1;
  a=i;
  cout<<"Value of i before decrement operation is "<<i<<"."<<endl;
  cout<<"Value of a before decrement operation is "<<a<<"."<<endl;
  
  //decrementing i and assigning its value to a
  a=--i;
  
  //printing value of a and i
  cout<<"Value of a after decrement operation is "<<a<<"."<<endl;
  cout<<"Value of i after decrement operation is "<<i<<"."<<endl;
  return 0;
}

Output:

Value of i before decrement operation is 1.
Value of a before decrement operation is 1.
Value of a after decrement operation is 0.
Value of i after decrement operation is 0.

Here, you can notice how i is decremented and then its value is assigned to variable a which is printed afterward.

Post-decrement Operator

A post-decrement operator uses the current value of a variable in the given expression before decrementing it. See the below code and explanation.

#include <iostream>
using namespace std;

int main()
{
  int a,i=1;
  a=i;
  cout<<"Value of i before decrement operation is "<<i<<"."<<endl;
  cout<<"Value of a before decrement operation is "<<a<<"."<<endl;
 
  //decrementing i using post decrement operator
  a=i--;
 
  //printing values of a and i
  cout<<"Value of a after decrement operation is "<<a<<"."<<endl;
  cout<<"Value of i after decrement operation is "<<i<<"."<<endl;
  return 0;
}

Output:

Value of i before decrement operation is 1.
Value of a before decrement operation is 1.
Value of a after decrement operation is 1.
Value of i after decrement operation is 0.

In the above code, the value of the variable i is first assigned to a and then decremented making the output differ from the previous example.

Thank you.

You may also read:

• Ternary Operator in C++