Converting int to binary String in C - c

Question

I'm trying to convert an integer to a binary String (see code below). I've already looked at several similar code snippets, and can't seem to find the reason as to why this does not work. It not only doesn't produce the correct output, but no output at all. Can somebody please explain to me in detail what I'm doing wrong?
#include <stdio.h>
#include <stdlib.h>
char* toBinaryString(int n) {
char *string = malloc(sizeof(int) * 8 + 1);
if (!string) {
return NULL;
}
for (int i = 31; i >= 0; i--) {
string[i] = n & 1;
n >> 1;
}
return string;
}
int main() {
char* string = toBinaryString(4);
printf("%s", string);
free(string);
return 0;
}

Answer 1

The line
string[i] = n & 1;
is assigning integers 0 or 1 to string[i]. They are typically different from the characters '0' and '1'. You should add '0' to convert the integers to characters.
Also, as #EugeneSh. pointed out, the line
n >> 1;
has no effect. It should be
n >>= 1;
to update the n's value.
Also, as #JohnnyMopp pointed out, you should terminate the string by adding a null-character.
One more point it that you should check if malloc() succeeded. (It is done in the function toBinaryString, but there is no check in main() before printing its result)
Finally, It doesn't looks so good to use a magic number 31 for the initialization of for loop while using sizeof(int) for the size for malloc().
Fixed code:
#include <stdio.h>
#include <stdlib.h>
char* toBinaryString(int n) {
int num_bits = sizeof(int) * 8;
char *string = malloc(num_bits + 1);
if (!string) {
return NULL;
}
for (int i = num_bits - 1; i >= 0; i--) {
string[i] = (n & 1) + '0';
n >>= 1;
}
string[num_bits] = '\0';
return string;
}
int main() {
char* string = toBinaryString(4);
if (string) {
printf("%s", string);
free(string);
} else {
fputs("toBinaryString() failed\n", stderr);
}
return 0;
}

Answer 2

The values you are putting into the string are either a binary zero or a binary one, when what you want is the digit 0 or the digit one. Try string[i] = (n & 1) + '0';. Binary 0 and 1 are non-printing characters, so that's why you get no output.

Answer 3

#define INT_WIDTH 32
#define TEST 1
char *IntToBin(unsigned x, char *buffer) {
char *ptr = buffer + INT_WIDTH;
do {
*(--ptr) = '0' + (x & 1);
x >>= 1;
} while(x);
return ptr;
}
#if TEST
#include <stdio.h>
int main() {
int n;
char str[INT_WIDTH+1]; str[INT_WIDTH]='\0';
while(scanf("%d", &n) == 1)
puts(IntToBin(n, str));
return 0;
}
#endif