Trying to understand C++ if syntax

[Straikkeri]

I've done some courses in Visual Basic and a lot more in Java. Now I've just begun learning C++, except this time I'm teaching myself. I've run in a snag with the very basic if statements of C++. I've always used if statements with clear logic: if x is something, do something. However, in C++ I keep running in to if statements that don't necessarily contain operators at all, or have function calls in them which also is a new thing for me. For instance:

  if(SomeBoolReturningFunc())
{
    //do some stuff
    //do some more stuff
}

I don't understand the logic how that is an if statement. I see a function call, but I don't see the terms of the If itself.

Then:

bool AwesomeResult = SomeBoolReturningFunc();
if(AwesomeResult)
{
    //do some other, more important stuff
}

I don't understand how a single variable can be considered an if statement. In java I would have done something like if (AwesomeResult = true) then stuff, to me that makes sense. Can anyone help me out and paraphrase this for me, thank you very much :)

[N36fSL3A]

If statements just execute if he value is true. You could actually just write true in there.

[vasilenko93]

http://www.cplusplus.com/doc/tutorial/program_structure/

An if statement takes a bool as an argument, so when you type something like if( x > y ), what really happens is the greater-then operator ( > ) returns ether a true or false. If its true then the if statement goes into the if body, if its false it continues.

Here is an example.

#include <iostream>
using namespace std;

bool isNegative( int number )
{
    if( number < 0 )  //"<" will return true if that is correct, false if not.
        return true;    //if false was returned above this code runs
    else  
        return false;  //else 
}

int main()
{
    if( isNegative( -5 ) )  //if accepts a boolean for argument, isNegative returns boolean
        cout << "Is negative" << endl;
    else 
        cout << "Is positive" << endl;
    return 0;
}

[Straikkeri]

Thank you very much for clearing that up. I see it's essentially the very same thing as what I would've done in java, except shorter. Also thanks for the very detailed example :)

So if I'm understanding right, what's happening in this line of code taken from a book I'm reading, is that a function named InitInstance is being called from within an if statement with two parameters. The function returns either 0 (false) or 1 (true). As it is written with an (!) operator, if the function returns something that does not equal true, then return 0 and end the program.

If (!InitInstance (hInstance, nCmdShow)) return 0;

Very basic stuff apparently, I just got confused as I would have written the same thing else wise more something like this

boolean myVariable = InitInstance (hInstance, nCmdShow);

if (myVariable = true) then

stuff.

Didn't realize you could do a function call inside an if statement and at the same time see if it's true or not without equaling it against something with an operator.

[N36fSL3A]

Make sure you put == instead of =.

[xismn]

conditional control structures such as if or the ternary operator implicitly compare the truth-ness of an expression by default.

Anything you provide these control structures with as conditions are actually expressions.

in your example, if not the value returned by InitInstance() is a non-zero value is true, execute the control structure body.

[long double main]

I don't understand how a single variable can be considered an if statement. In java I would have done something like if (AwesomeResult = true)

(First of all, you're missing a second equals sign there.)

Doesn't the same thing work in Java as well?
http://ideone.com/sXDxFB

[Straikkeri]

Yes I am (missing another equals sign that is) :) And if it does work, I've never seen or used it that way myself but this stuff is good to know :)