1. Set or Clear a Specific Bit in a Register

#include <stdio.h>

unsigned char modifyBit(unsigned char reg, int pos, int mode) {
    // mode | bit | new value
    //   0.    0.     0
    //   0.    1.     0
    //   1.    0.     1
    //   1.    1.     1

    if (mode == 0) return reg & ~(1 << pos);
    else 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;
}