Bit manipulation in C

bits.c

#include "bits.h"

const int NUM_BITS_IN_BYTE = 8;

int getbit(char c, int i) {
    if (i >= NUM_BITS_IN_BYTE || i < 0) {
        return -1;
    }
    return (c & (1 << i)) > 0;
}

void setbit(char *c,int i) {
    if (i >= NUM_BITS_IN_BYTE || i < 0) {
        return;
    }
    *c = ((char)(1 << i)) | *c;
}

void unsetbit(char *c, int i) {
    if (i >= NUM_BITS_IN_BYTE || i < 0) {
        return;
    }
    *c = ~((char)(1 << i)) & *c;
}

void getbitstr(char c, char *s) {
    for (int i = 0; i < NUM_BITS_IN_BYTE; ++i) {
        s[NUM_BITS_IN_BYTE-1-i] = getbit(c, i) > 0 ? '1' : '0';
    }
}

bits.h

#ifndef BITS_H
#define BITS_H

int getbit(char c, int i);

void setbit(char *c,int i);

void unsetbit(char *c, int i);

void getbitstr(char c, char *s);

#endif

main.c

#include <stdio.h>
#include "bits.h"

int main(int argc, char const *argv[]) {
    char a = 1 << 4; // 0001 0000
    a = a - 1;       // 0000 1111
    setbit(&a, 5);   // 0010 1111 
    setbit(&a, 7);   // 1010 1111
    unsetbit(&a, 2); // 1010 1011

    char s[9] = {0};
    for (int i = sizeof(a)-1; i >= 0; --i) {
        char *c = ((char *)&a);
        getbitstr(*(c + i), s);
        printf("%s", s);
    }
    printf("\n");

    return 0;
}

Run with:
gcc -c *.c; gcc *.o; ./a.out