Increment and Decrement Operators in C

The increment(++) and decrement(--) operators are unary operators that increment and decrement value of a variable by 1.

++x is equivalent to x = x + 1
- -x is equivalent to x = x - 1

Increment and decrement operators must be used only with a variable not with constants or expressions. For example:

int x = 1, y = 1, z = 1; ++x; /* valid - increment operator operating on a variable */ ++7 /* invalid - increment operator operating on a constant value */ ++(x-y+z) /* invalid - increment operator operating on an expression */

Increment/Decrement operators are of two types:

Prefix increment/decrement operator

Postfix increment/decrement operator

Prefix Increment/Decrement Operator

In Prefix increment/decrement operator, first the value of variable is incremented/decremented then the new value is used in the operation.

Example: Prefix Increment

Let's take a variable x whose value is 5.

The statement:

y = ++x;

means first increment the value of x by 1 then assign the value of x to y. This single statement is equivalent to these two statements:

x = x + 1; y = x;

Now value of x is 6 and value of y is also 6.

Example: Prefix Decrement

Let's take a variable x whose value is 5.

The statement:

y = --x;

means first decrement the value of x by 1 then assign the value of x to y. This single statement is equivalent to these two statements:

x = x - 1; y = x;

Now value of x is 4 and value of y is also 4.

The following program demonstrates prefix increment/decrement operator.

#include <stdio.h> int main(void) { int x = 5, y = 1; printf("Initial value of x = %d\n", x); /* Print the initial value of x */ printf("Initial value of y = %d\n\n", y); /* Print the initial value of y */ y = ++x; /* Increment the value of x by 1 then assign the value of x to y */ printf("After incrementing by 1: x = %d\n", x); printf("Value of y = %d\n\n", y); y = --x; /* Decrement the value of x by 1 then assign the value of x to y */ printf("After decrementing by 1: x = %d\n", x); printf("Value of y = %d\n\n", y); return 0; }

Output:

Initial value of x = 5 Initial value of y = 1 After incrementing by 1: x = 6 Value of y = 6 After decrementing by 1: x = 5 Value of y = 5

Postfix Increment/Decrement operator

In postfix Increment/Decrement operator, first the value of variable is used in the operation and then increment/decrement takes place.

Example: Postfix Increment

Let's take a variable x whose value is 5.

The statement:

y = x++;

means first the value of x is assigned to y and then x is incremented. This single statement is equivalent to these two statements:

y = x; x = x + 1;

Now value of x is 6 and value of y is 5.

Example: Postfix Decrement

Let's take a variable x whose value is 5.

The statement:

y = x--;

means first the value of x is assigned to y and then x is decremented. This single statement is equivalent to these two statements:

y = x; x = x - 1;

Now value of x is 4 and value of y is 5.

The following program demonstrates postfix increment/decrement operator.

#include <stdio.h> int main(void) { int x = 5, y = 1; printf("Initial value of x = %d\n", x); /* Print the initial value of x */ printf("Initial value of y = %d\n\n", y); /* Print the initial value of y */ y = x++; /* First assign the value of x to y and then increment the value of x by 1 */ printf("After incrementing by 1: x = %d\n", x); printf("Value of y = %d\n\n", y); y = x--; /* First assign the value of x to y and then decrement the value of x by 1 */ printf("After decrementing by 1: x = %d\n", x); printf("Value of y = %d\n\n", y); return 0; }