Pre-Increment and Post-Increment Concept in C/C++

Both pre-increment and post-increment are used to represent the expression of increasing a value by adding 1. Their behavior are different because pre-increment (++i) increases the value before it is used in an expression, while post-increment (i++) increases it after.

Below is the key-terms of pre-increment and post-increment in C/C++:

• Pre-increment (++i) : Before assigning the value to the variable, the value is incremented by one.
• Post-increment (i++) : After assigning the value to the variable, the value is incremented.

Syntax of Using Pre and Post Increment Operators

The following is the basic syntax of pre-increment and post-increment in C/C++:

// Pre-increment
++variable_name; 

// Post-increment
variable_name++; 

Here,

• variable_name : This is name of the variable given by user.

Pre Increment Operator (x++)

Pre-increment operator increments the value of a variable by 1 before it is used in the expression.

Example

Here, 'x' is 5, then 'y' will be 6 because 'x' is increased before it's used in the expression:

#include <stdio.h>

int main() {
int x = 5;
int y = ++x;  
        
printf("Value of x: %d\n", x);
printf("Value of y: %d\n", y);
        
return 0;
}        

Value of x: 6
Value of y: 6    

#include <iostream>
using namespace std;
            
int main() {
   int x = 5;
   int y = ++x;  
            
   cout << "Value of x: " << x << endl;
   cout << "Value of y: " << y << endl;
            
return 0;
}   

Value of x: 6
Value of y: 6    

Post Increment Operator (x++)

Post-increment operator increments the value of a variable by 1 after using it in the expression.

Example

In this program, y is assigned the value of x before it is incremented because the post-increment operator (x++) is used.

#include <stdio.h>

int main() {
int x = 5;
int y = x++;  // Post-increment: y is assigned x (5), then x is incremented
        
printf("Value of x: %d\n", x);
printf("Value of y: %d\n", y);
        
return 0;
}        

Value of x: 6
Value of y: 5

#include<iostream>
using namespace std;
        
int main() {
int x = 5;
int y = x++;  // y gets 5, then x becomes 6
        
cout << "Value of x: " << x << endl;
cout << "Value of y: " << y << endl;
        
return 0;
}

Value of x: 6
Value of y: 5

Now, let us look into the tabular structure of pre-incremental and post-incremental to remember the concept: