How to find mantissa length on a particular machine

float a = 1;
float b = 0.5;
int bits = 0;
while (a + b != a) {
    bits = bits + 1;
    b = b / 2;
}

#include <stdio.h>
#include <float.h>

int main(void) {
    float a = 1;
    float b = 0.5;
    float c = a + b;
    int bits = 1;
    while (c != a) {
        bits = bits + 1;
        b = b / 2;
        c = a + b;
    }
    printf("%dn",FLT_MANT_DIG);
    printf("%dn",bits);
    return 0;

#include <iostream>
#include <limits>
#include <typeinfo>

template <typename T>
void printDetailsFor() {
    std::cout
    	<< "Printing details for " << typeid(T).name() << ":n"
    	<< "tradix:        " << std::numeric_limits<T>::radix        << "n"
    	<< "tradix digits: " << std::numeric_limits<T>::digits       << "n"
    	<< "tepsilon:      " << std::numeric_limits<T>::epsilon()    << "n"
    	<< std::endl;
}

int main() {
    printDetailsFor<int>();
    printDetailsFor<float>();
    printDetailsFor<double>();
    printDetailsFor<long double>();
    return 0;
}

Printing details for i:
    radix:        2
    radix digits: 31
    epsilon:      0

Printing details for f:
    radix:        2
    radix digits: 24
    epsilon:      1.19209e-07

Printing details for d:
    radix:        2
    radix digits: 53
    epsilon:      2.22045e-16

Printing details for e:
    radix:        2
    radix digits: 64
    epsilon:      1.0842e-19