C/C++ casting different with function versus expression?

Question

#include <stdio.h>

double metersToFeet(double meters)
{
    return meters / 0.3048;
}

int main()
{
    printf("%u\n", (unsigned char)(char)(45.72 / 0.3048));
    printf("%u\n", (unsigned char)(char)metersToFeet(45.72));
    return 0;
}

This program outputs (on both GCC and Clang):

127
150

Why am I getting two different numbers?

Answer 1

The real answer (150) exceeds the range of a char (on a normal system) if it's signed. This conversion invokes undefined behaviour; the compiler is free to do whatever it likes.

From the C99 standard, 6.3.1.4:

When a finite value of real floating type is converted to an integer type other than _Bool, the fractional part is discarded (i.e., the value is truncated toward zero). If the value of the integral part cannot be represented by the integer type, the behavior is undefined.