Setting Bits in C (original) (raw)

Last Updated : 16 Oct, 2024

In C programming, setting a bit is the process of setting a specific bit of a binary number to 1. This operation is crucial in various applications, including memory management, data processing, and hardware control.

In this article, we will learn how to set a bit at a given position in a binary number. We will also explore how to set multiple bits simultaneously.

Table of Content

How to Set a Bit in C?
Setting a Specific Bit in C
Setting Multiple Bits in C
Setting Bits in C - FAQs

How to Set a Bit in C?

Setting a bit means setting its value to 1. In C, we can set a given bit using the OR operator (|) combined with a bit mask. Below is the truth table of OR:

Truth-Table-for-OR-Operation

From the above table, we can infer that:

By ORing a bit with 1, the given bit is set to 1.
By ORing a bit with 0, the given bit remains unchanged.

Setting a Specific Bit in C

To set a specific bit in a number, you can use a bit mask with the OR operator. In that bitmask number, only the bit you want to set is set to 1, and all other bits are set to 0.

Example:

**Input: binary_number: 01100111
bit to set: 5th
**Output: binary_number: 01100111
mask_used: 00100000

C `

// C Program to Set a given bit of a binary number #include <stdio.h>

int main() { // Binary: 01100111 unsigned int num = 103;

// Setting the 5th bit (0-based index)
unsigned int bit_position = 5;

// Create a mask with only the 5th bit set to 1
unsigned int mask = 1 << bit_position;

// Set the bit using OR
num = num | mask;

// Print the result
printf("Result: %u\n", num);

return 0;

}

**Time Complexity: O(1)
**Space Complexity: O(1)

Setting Multiple Bits in C

We can also set multiple bits by creating a mask with multiple bits set to 1. ORing the number with this mask will set all corresponding bits.

Example: Setting the 1st, 3rd, and 4th Bits

We can use the left shift operator to create a mask, but remember the 0-based indexing in the shifting.

C `

// C Program to Set multiple bits of a binary number #include <stdio.h>

int main() { // Binary: 01100111 unsigned int num = 103;

// Create a mask with the 1st, 3rd, and 4th bits set to
// 1
unsigned int mask = (1 << 0) | (1 << 2) | (1 << 3);

// Set the bits using OR
num = num | mask;

// Print the result
printf("Result: %u\n", num);

return 0;

}

**Time Complexity: O(n), where n is the number of bits to be set.
**Space Complexity: O(1)