Decimal to binary format on C.

dectobin.h

#include <cmath>

inline void dectobin(int indec, int len) {
    using namespace std;
    long ndec = indec % (long)(pow(2.0, len)); // truncating to max length!
    for (int i = len - 1; i >= 0; i--)
    {
        long pw = (long)pow(2.0, i);
        if (ndec - pw >= 0) {
            printf("1");
            ndec -= pw;
        }
        else {
            printf("0");
        }
    }
}