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Thinking in C++
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Recursion is an interesting and sometimes useful programming technique whereby you call the function that you’re in. Of course, if this is all you do, you’ll keep calling the function you’re in until you run out of memory, so there must be some way to “bottom out” the recursive call. In the following example, this “bottoming out” is accomplished by simply saying that the recursion will go only until the cat exceeds ‘Z’:[31]

//: C03:CatsInHats.cpp
// Simple demonstration of recursion
#include <iostream>
using namespace std;

void removeHat(char cat) {
  for(char c = 'A'; c < cat; c++)
    cout << "  ";
  if(cat <= 'Z') {
    cout << "cat " << cat << endl;
    removeHat(cat + 1); // Recursive call
  } else
    cout << "VOOM!!!" << endl;

int main() {
} ///:~

In removeHat( ), you can see that as long as cat is less than ‘Z’, removeHat( ) will be called from within removeHat( ), thus effecting the recursion. Each time removeHat( ) is called, its argument is one greater than the current cat so the argument keeps increasing.

Recursion is often used when evaluating some sort of arbitrarily complex problem, since you aren’t restricted to a particular “size” for the solution – the function can just keep recursing until it’s reached the end of the problem.

Thinking in C++
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   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire