Programming and Graphics

3.10 Preprocessor define and undefine 89

#define print cout<<

int main()

{

stringa="hello";

print a;

print endl;

return 0;

}

Running the code prints on the screen:

hello

The preprocessor has substituted the C++ command “cout <<” for every in-
stance of the “print” statement in the code. Effectively, “print” has become
a macro for “cout <<”.

A macro can be removed at any time using theundef preprocessor
directive. As an example, consider the code:

#include <iostream>

using namespace std;

#define print cout <<

int main()

{

#define eol << endl

string a = "hello";

print a eol;

#undef eol

#define eol << " for your business" << endl

string b = "thank you";

print b eol;

return 0;

}

Running the code prints on the screen:

hello

thank you for your business

Thedefinepreprocessor directive may also be used to implement simple
functions. For example, the block of commands:

#define square(x) x*x;

double e = 5.0;