Weird C++ float bug

Question

#include <iostream>
using namespace std;

int main()
{
    cout.precision(32);

    float val = 268433072;
    float add = 13.5;

    cout << "result =" << (val + add) << endl;
}

I'm compiling the above program with standard g++ main.cc
and running it with ./a.out

The ouput I receive however, is,
result =268433088

Clearly, this is not the correct answer..Why is this happening?

EDIT: This does not occur when using double in place of float

Answer 1

You can reproduce your "float bug" with an even simpler piece of code

#include <iostream>
using namespace std;

int main()
{
    cout.precision(32);
    float val = 2684330722;
    cout << "result =" << val << endl;
}

The output

result =2684330752

As you can see the output does not match the value val was initialized with.

As it has been stated many times, floating-point types have limited precision. Your code sample simply exceeded that precision, so the result got rounded. There's no "bug" here.