How can I store value in bit in C language

This question already has an answer here:

How do you set, clear, and toggle a single bit? 26 answers

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You need to calculate a byte offset and a bitmask within that byte.

Set the bit: bitwise OR with mask

Clear the bit: bitwise AND with complement of mask

Read the bit: return bitwise AND of byte and mask

The code:

void set_bit(char *buf, int bit, int val)
{
    int byte = bit / 8;
    char mask = 1 << (bit % 8);
    if (val)
        buf[byte] |= mask;
    else
        buf[byte] &= ~mask;
}

int get_bit(char *buf, int bit)
{
    int byte = bit / 8;
    char mask = 1 << (bit % 8);
    return buf[byte] & mask ? 1 : 0; 
}

Example: Set bit 17 to 1. Byte offset is 17/8 = 2 . Bit offset is 17%8 = 1 . The bitmask is generated by left-shifting 1 by the bit offset: results in 00000010 binary. Bitwise OR byte[2] with it: all bits remain the same, except where the mask bit is 1.

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