C语言如何将相应的整数转换为二进制

请问这个要怎么解决？应该是 输入整数，返回相应的16 个字符。在“PUT YOUR CODE HERE”写内容，蟹蟹大lao。题目如下

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#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <assert.h>

#define N_BITS 16

char *sixteen_out(int16_t value);

int main(int argc, char *argv[]) {

    for (int arg = 1; arg < argc; arg++) {
        long l = strtol(argv[arg], NULL, 0);
        assert(l >= INT16_MIN && l <= INT16_MAX);
        int16_t value = l;

        char *bits = sixteen_out(value);
        printf("%s\n", bits);

        free(bits);
    }

    return 0;
}

// given a signed 16 bit integer
// return a null-terminated string of 16 binary digits ('1' and '0')
// storage for string is allocated using malloc
char *sixteen_out(int16_t value) {

    // PUT YOUR CODE HERE

}