Migrating to C++ from Pascal/SCAR/Delphi? Look here for a cool trick.

If you're used to using Pascal-based languages such as SCAR or Delphi, you're probably familiar with the syntax of a repeat-until loop. While C/C++ has no innate support for an equivalent to a repeat-until loop, it is possible to use preprocessor macros to create one.

See here:

Code:

#include <iostream>
using namespace std;

#define REPEAT do{
#define UNTIL(expr) }while(!(expr))

int main(int argc, char *argv[])
{
	int i = 0;
	REPEAT
		cout << "i: " << i << endl;
		i++;
	UNTIL(i==10);
	return 0;
}

Macros created with the define statement are replaced with actual code when they are compiled. For example, if you were to save and view the intermediate (processed, .ii) C++ source file, the main() function would be:

Code:

int main(int argc, char *argv[])
{
	int i = 0;
	do{
		cout << "i: " << i << endl;
		i++;
	}while(!(i==10));
	return 0;
}

It works just as you would expect it to. This is just a source, not a tutorial, so I won't go any more in depth on it. If you already know general programming concepts this shouldn't be hard.

 

That's really neat, I wouldn't of thought of that. It's also good that you showed what it actually compiles to so that anyone referring to this realizes that a REPEAT UNTIL is basically just a do while(not(blabla)).

 

Or just:

Code:

for (i=0,  i < 10, i++);
{
cout << "i: " << i << endl;
}

or

Code:

int i = 0

while(i<10);
{
cout << "i: " << i << endl;
i++
}

What you did looks like it'd take longer to code...

#define is used if you don't want to type out a long piece of code if you're going to be using it a lot, such as #define CAST(expr) static_cast<unsigned int long>(expr)

 

It can also be used to 'imagine' that you still have repeat/until, for coders who are comfortable with that sort of loop.

 

Yeah, I got that part but obviously the guy above you didn't because he tried to tell you two more effective ways of coding what you posted. Your point was not the time efficiency or coding ease needed to do it.

 

Exactly.

 

it would be cool for someone to make an include so you can make c++ coding like scar eg.
WriteLn("Hello World");
instead of
cout << "Hello World\n";