1. Set or Clear a Specific Bit in a Register

#include <stdio.h>

unsigned char modifyBit(unsigned char reg, int pos, int mode) {
    // Write your code here
    if(mode==1){
        reg |= 0x01<<pos;
    }
    else{
        reg &=~(0x01<<pos);
    }
    return reg;
}

int main() {
    unsigned char reg;
    int pos, mode;
    scanf("%hhu %d %d", &reg, &pos, &mode);  // <-- replaced ® with &reg

    unsigned char result = modifyBit(reg, pos, mode);
    printf("%hhu\n", result);
    return 0;
}

bitwise or to set

bitwise and a not to clear