Difference Between Increment and Decrement Operators in C

Prerequisite: Operators in C/C++

1) Increment Operators: The increment operator is used to increment the value of a variable in an expression. In the Pre-Increment, the value is first incremented and then used inside the expression. Whereas in the Post-Increment, the value is first used inside the expression and then incremented. 

Syntax:

// PREFIX
++m

// POSTFIX
m++

where m is a variable

Example:

C

#include <stdio.h>

int increment(int a, int b)
{
    a = 5;

    // POSTFIX
    b = a++;
    printf("%d", b);

    // PREFIX
    int c = ++b;
    printf("\n%d", c);
}

// Driver code
int main()
{
    int x, y;
    increment(x, y);

    return 0;
}

Output:

5
6

2) Decrement Operators: The decrement operator is used to decrement the value of a variable in an expression. In the Pre-Decrement, the value is first decremented and then used inside the expression. Whereas in the Post-Decrement, the value is first used inside the expression and then decremented. 

Syntax:

// PREFIX
--m

// POSTFIX
m--

where m is a variable

Example:

C

#include <stdio.h>

int decrement(int a, int b)
{
    a = 5;

    // POSTFIX
    b = a--;
    printf("%d", b);

    // PREFIX
    int c = --b;
    printf("\n%d", c);
}

// Driver code
int main()
{
    int x, y;
    decrement(x, y);

    return 0;
}

Output:

5
4

Differences between Increment And Decrement Operators

Increment Operator	Decrement Operator
Increment Operator adds 1 to the operand.	Decrement Operator subtracts 1 from the operand.
Postfix increment operator means the expression is evaluated first using the original value of the variable and then the variable is incremented(increased).	Postfix decrement operator means the expression is evaluated first using the original value of the variable and then the variable is decremented(decreased).
Prefix increment operator means the variable is incremented first and then the expression is evaluated using the new value of the variable.	Prefix decrement operator means the variable is decremented first and then the expression is evaluated using the new value of the variable.
Generally, we use this in decision-making and looping.	This is also used in decision-making and looping.