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c++operatorsinequalityrelational-operators

Why does the following inequality evaluate to true in C++?

The following piece of code seems so trivial. I don't understand why its not working.

float bound_min   = +314.53f;
float bound_max   = +413.09f;
float my_variable = -417.68f;

if (bound_min <= my_variable <= bound_max)
{
    printf("Why on earth is this returning True?");
}

Can a C++ wizard of stackoverflow please come and rescue me?

Solution

  • The condition in the if statement

    if (bound_min <= my_variable <= bound_max)

    is equivalent to

    if ( ( bound_min <= my_variable ) <= bound_max)

    The first subexpression ( bound_min <= my_variable ) evaluates to boolean false.

    So as a result you have

    if ( false  <= bound_max)

    In this result expression the boolean false is converted to the integer 0 due to the integral promotions.

    if ( 0 <= bound_max)

    So the final value of the condition is true.

    From the C++ 17 Standard (8.9 Relational operators)

    1 The relational operators group left-to-right. 

    [Example: a<b<c means (a<b)<c and not (a<b)&&(b<c) —end example] .