C++ Recursion - Notes | Study C++ Programming for Beginners - Class 8

• Recursion is the technique of making a function call itself. This technique provides a way to break complicated problems down into simple problems which are easier to solve.
• Recursion may be a bit difficult to understand. The best way to figure out how it works is to experiment with it.

Adding two numbers together is easy to do, but adding a range of numbers is more complicated. In the following example, recursion is used to add a range of numbers together by breaking it down into the simple task of adding two numbers:

Example

int sum(int k) {

  if (k > 0) {

    return k + sum(k - 1);

  } else {

    return 0;

  }

}

int main() {

  int result = sum(10);

  cout << result;

  return 0;

}

When the sum() function is called, it adds parameter k to the sum of all numbers smaller than k and returns the result. When k becomes 0, the function just returns 0. When running, the program follows these steps:

10 + sum(9)

10 + ( 9 + sum(8) )

10 + ( 9 + ( 8 + sum(7) ) )

...

10 + 9 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1 + sum(0)

10 + 9 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1 + 0

Since the function does not call itself when k is 0, the program stops there and returns the result.