Explain recursive algorithms

[-TesseracT-]

I am REALLY lost when it comes to these. 

 

Please solve this problem in a C-language with a recursive algorithm. https://projecteuler.net/problem=2

It's incredibly easy to do but I don't know how to use recursive algorithms. Also maybe explain  everything in simple terms so that I can understand. I'm just lost when it comes to learning new things in programming.

[alpenwasser]

I have found that the best way to understand recursion for me was to take pen and

paper and a recursion program and run through a few scenarios step by step. It's

a slow process, but it has worked well for me.

As an example, take this Fibonacci C program:

#include<stdio.h> int Fibonacci(int); main(){   int n, i = 0, c;    scanf("%d",&n);    printf("Fibonacci series\n");    for ( c = 1 ; c <= n ; c++ )   {      printf("%d\n", Fibonacci(i));      i++;    }    return 0;} int Fibonacci(int n){   if ( n == 0 )      return 0;   else if ( n == 1 )      return 1;   else      return ( Fibonacci(n-1) + Fibonacci(n-2) );}

source: http://www.programmingsimplified.com/c-program-generate-fibonacci-series

In principle, recursion is pretty simple. An initial function call is made,

and then the function keeps calling itself with different arguments unless

some break condition is met. The parent functions stay open and wait until

they get a return value from their child or children.

So, in this case, unless the argument Fibonacci() gets is zero or one, it will

take its argument, decrease it by one and two respectively, and call two child

functions with those arguments, then it will wait until it gets the return

values from those functions. The function calls which are made with zero and

one will no longer spawn child functions, but instead will return a value,

which will allow their parent to return a value, which will allow the

grandparent to return a value and so on until the initial caller gets its

return values, is able to do the final computation and then returns the value

we are actually looking for.

For a better understanding, I sincerely recommend playing this through with

pen and paper and some examples. Maybe try to map out the function calls and

the current values etc. in a tree, then you should get a pretty clear picture

of what it's about. I also tend to do this when I write more complicated

recursive code than the example above (for example, I once wrote a program

which needed to traverse the filesystem, which is another classic example for

recursion).

[-TesseracT-]

Thank you good sir!