1. Set or Clear a Specific Bit in a Register

#include <stdio.h>

unsigned char modifyBit(unsigned char reg, int pos, int mode) {
    if(reg != 0 && (pos >= 0 && pos <= 7) && (mode == 0 || mode ==1))
    {
        if(mode == 0)
            reg = reg & (~(1 << pos));
        else
            reg = reg | (1 << pos);

        return reg;
    }
    else
        return 0;
}

int main() {
    unsigned char reg;
    int pos, mode;
    scanf("%hhu %d %d", &reg, &pos, &mode);
    printf("%d", modifyBit(reg, pos, mode));
    return 0;
}