Beginner's question about functions.

I'm trying to study how the functions in C work.

First: Does anyone has any good book that deals specifically with functions in C?

I'm very puzzled about the recursiveness of functions and how it really works. How exactly a function calls itself (with other values) when it's inside itself and how the values change.

For example in the following code............:

Code:

---

#include "stdio.h"
#define max(a,b) (a)>(b)? a : b

int g=0;
int ab(int n, int a)
{
    if (n==0) return 5;

    printf("a=.....%d\n",a);
    printf("g=.....%d\n",g);
    printf("-------------\n");
   
    g=-50;
    a-=1;
   
    g=max(g,ab(n-1,a));
   
    printf("a(%d)==========%d\n",n,a);
   
    return g;
}

void main(void)
{
        ab(2,10);
}

---

........... i had the impression that it should return the output:

a=.....10
g=.....0
-----------------
a=.....9
g=.....-50
-----------------
a(1)========8
a(2)========9


But instead it returns the output:

a=.....10
g=.....0
-----------------
a=.....9
g=.....-50
-----------------
a(1)========8
a=.....9
g=.....5
-----------------
a(1)========8
a(2)========9


Why it does that?
Can anyone explain step by step why it prints the extra(red) lines?

Because you are calling ab() inside itself, and ab() produces that sort of output?

--
Mats

Okay, think about this:

Code:

---

#include "stdio.h"
#define max(a,b) (a)>(b)? a : b

int g=0;

int testfunc (int X, int Y) {
        return max(X,Y);
}

int ab(int n, int a)
{
    if (n==0) return 5;

    printf("a=.....%d\n",a);
    printf("g=.....%d\n",g);
    printf("-------------\n");
   
    g=-50;
    a-=1;
   
    g=testfunc(g,ab(n-1,a));
   
    printf("a(%d)==========%d\n",n,a);
   
    return g;
}

void main(void)
{
        ab(2,10);
}

---

Produces the expected:
a=.....10
g=.....0
-------------
a=.....9
g=.....-50
-------------
a(1)==========8
a(2)==========9
ps. look for stuff about the Fibonacci set, that is the essential form of recursion I think

Main returns int; not void.

Quote:

---

Does anyone has any good book that deals specifically with functions in C?

---

try Tanenbaum-data structures using c & c++.it deals with recursive functions in great detail.