Thread: Issues

& is the address operator.. most commonly used for storing a variable address into a pointer. && is the 'and' boolean expression.. use mostly for if, if/else, if/else if logical flow control.

Code:

     double *double_ptr;     //Declare 'double_ptr' as a pointer-type variable

     double_ptr = &result;    //Store the address of 'result' into a pointer

      cout << *double_ptr;  //Use the '*' dereferrencing operator when you want to see what the pointer points to

vs. the && and operator

Code:

if ((choice == 0) && (result > 0))

      answer++;

and couldnt see int main();

You don't need to prototype main.

Quzah.

> & is the address operator..
It is also the bitwise-AND operator, which is similar to the boolean-AND you've already mentioned.

Code:

int a = 0x1234;
a = a & ~0xF;   // lose the bottom 4 bits = 0x1230

If you write

Code:

if ( a & b )

You wrote

Code:

if ( (a & b) != 0 )

Which is valid to do, and if a and b are boolean, you get the same answer whether you use & or &&.

The really big difference is that logical operations && and || use short-circuit evaluation, meaning the remainder of the expression is not evaluated if the result is already known.
Eg.

Code:

if ( foo() & bar() ) 
if ( foo() && bar() )

In case 1, foo() and bar() will both be called, and it is undefined as to which one is called first. Normal expression evaluation rules apply.
In case 2, foo() is always called first, and bar() is only called if foo() returned true.

This means you can test and dereference a pointer in the same expression with perfect safety.

Code:

int isNonEmptyString ( char *s ) {
  if ( s != NULL && *s != '\0' )
    return 1;
  else
    return 0;
}

Maybe one of the functions you are using is implemented a different way in WinNT and the compiled code therefore is calling a non-existant function on Win9x.

As to why it would work on both platforms after being compiled on the older Win9x, WinNT needs to be compatible with older software and therefore supports the Win9x method.

> if (fileExists("C:/Windows") & fileExists("C:/Winnt"))
The windows environment variable "windir" tells you the windows installation directory

Something along the lines of

Code:

char *winroot = getenv( "windir" );
if ( winroot != NULL ) {
} else {
  // start guessing, or complain
}