1. Set or Clear a Specific Bit in a Register

#include <stdio.h>
unsigned char modifyBit(unsigned char reg, int pos, int mode) {
    if (mode)
        return reg | (1<<pos);
    return reg & ~(1<<pos);    
}
int main() {
    unsigned char reg;
    int pos, mode;
    scanf("%hhu %d %d", &reg, &pos, &mode);
    printf("%d", modifyBit(reg, pos, mode));
    return 0;
}

  mode 1 : that is to set bit

doing OR operation is to set the particular bit by left shifting to that position.

mode 0: that is to clear bit

doing AND operation with 0 at that particular position, 

inorder to do that we first shift 1 to that particular position then compliment all the bits.later do AND operation with register.