Increment and Decrement Operators in C

The increment ( ++ ) and decrement ( -- ) operators in C are unary operators for incrementing and decrementing the numeric values by 1, respectively. They are one of the most frequently used operators in programming for looping, array traversal, pointer arithmetic, and many more.

Increment Operator in C

The increment operator ( ++ ) is used to increment the value of a variable in an expression by 1. It can be used on variables of the numeric type, such as integer, float, character, pointers, etc.

The Increment Operator in C can be used in two ways, either as a prefix (pre-increment) or a postfix (post-increment).

Syntax:

// AS PREFIX
++m

// AS POSTFIX
m++

where m is variable. Both pre-increment and post-increment increase the value of the variable but there is a little difference in how they work.

1. Pre-Increment

In pre-increment, the increment operator is used as the prefix. Also known as prefix increment, the value is incremented first according to the precedence and then the less priority operations are done.

result = ++var1;

The above expression can be expanded as

var = var + 1;
result = var;

2. Post-Increment

In post-increment, the increment operator is used as the suffix of the operand. The increment operation is performed after all the other operations are done. It is also known as postfix increment.

result = var1++;

The above expression is equivalent

result = var;
var = var + 1;

Example of Increment Operator

#include <stdio.h>

void preincrement(int x)
{
    // PREFIX
    printf( "X = %d\n", x);
    int prefix = ++x;
    printf("Prefix Increment: %d\n", prefix);
}

void postincrement(int x)
{
    // POSTFIX
    printf( "X = %d\n", x);
    int postfix = x++;
    printf("Postfix Increment: %d", postfix);
}

int main()
{
    int x =5; 
    preincrement(x);
    postincrement(x);

    return 0;
}

X = 5
Prefix Increment: 6
X = 5
Postfix Increment: 5

As we can see in postfix, the value is incremented after the assignment operator is done.

Note: The post-increment has higher precedence that pre-increment as it is postfix operator while pre-increment comes in unary operator category.

Decrement Operator in C

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

Just like the increment operator, the decrement operator can also be used in two ways:

// AS PREFIX
--m

// AS POSTFIX
m--

where m is variable.

1. Pre-Decrement Operator

The pre-decrement operator decreases the value of the variable immediately when encountered. It is also known as prefix decrement as the decrement operator is used as the prefix of the operand.

result = --m;

which can be expanded to

m = m - 1;
result = m;

2. Post-Decrement Operator

The post-decrement happens when the decrement operator is used as the suffix of the variable. In this case, the decrement operation is performed after all the other operators are evaluated.

result = m--;

The above expression can be expanded as

result = m;
m = m-1;

Example of Decrement Operator

#include <stdio.h>

void predecrement(int x)
{
    // PREFIX
    printf( "X = %d\n", x);
    int prefix = --x;
    printf("Prefix Decrement: %d\n", prefix);
}
void postdecrement(int x)
{
    // POSTFIX
    printf( "X = %d\n", x);
    int postfix = x++;
    printf("Postfix Decrement: %d", postfix);
}

// Driver code
int main()
{
    int x =5; 
    predecrement(x);
    postdecrement(x);

    return 0;
}

X = 5
Prefix Decrement: 4
X = 5
Postfix Decrement: 5

Increment vs Decrement

The following table lists the major differences between increment and decrement operators in C :

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