Recursion

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SharpBASIC supports recursion for subroutines and functions. When using recursion, always keep in mind the following three basic rules:

• A recursive algorithm must call itself, recursively.

• A recursive algorithm must have a base case.

• A recursive algorithm must change its state and move toward the base case.

A base case is the condition that allows the algorithm to stop recursing.

A base case is typically a problem that is small enough to solve directly. In the factorial algorithm the base case is n=1. We must arrange for a change of state that moves the algorithm toward the base case. A change of state means that some data that the algorithm is using is modified. Usually the data that represents our problem gets smaller in some way. In the factorial n decreases.

Example of recursive factorial and fibonacci:

Code: Select all

decl func factorial(n: int): int;
decl func fibonacci(n: int): int;

dim n: int;
dim i: iter;

main do

  n = 5;

  print("factorial of 5:");
  print(factorial(n));
  print();

  print("fibonacci of 5:");

  for i = 0 to n - 1 :++ do
    print(fibonacci(i));
  end

  print();

end

func factorial(n: int): int
do
  if n == 0 do
    return 1;
  end

  factorial = n * factorial(n - 1);
end

func fibonacci(n: int): int
do
  when n is 0, 1 do
    return n;
  end

  fibonacci = (fibonacci(n - 1) + fibonacci(n - 2));
end

Output:

factorial of 5:
120

fibonacci of 5:
0
1
1
2
3