## Recursion

frank
Posts: 40
Joined: Sun Nov 21, 2021 12:04 pm
Location: Netherlands
Contact:

### Recursion

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 i, n: int;

main do

n = 5;

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

print("fibonacci of 5:");

count i up 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
Keep it simple!