## Recursion

frank
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Joined: Sun Nov 21, 2021 12:04 pm
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### 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 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
Last edited by frank on Wed Mar 09, 2022 2:46 pm, edited 1 time in total.
Keep it simple!