Thread: A fundamental question on 'return' statement

I've an extremely n00bish doubt regarding 'return' statement. If I comment out second last code in attoi function; the output is only '6'; instead of 123456 (I figured out the formatting portion to print 123456). Why does 'return' chooses to print only last element from the character array? Why does'nt it is returning a value for every iteration?

I hope I sound coherent?

Code:

#include <stdio.h>
#include <stdlib.h>

int attoi(char inp[]);

int main(void) {
	int l;
	char p[5] = {49,50,51,52,53,54};
	l = attoi (p);
	printf ("%d",l);
}
/* attoi: convert s to integer */
int attoi(char s[])
{
   int i, n;
   n = 0;
   for (i = 0; s[i] >= '0' && s[i] <= '9'; ++i)
   n = /*10 * n + */(s[i] - '0');
   return n;
}

A function only returns once for each call.

So it waits for loop to get over & returns the final value?

Originally Posted by Tibo-88

No, it will return the first time it reach the "return" statement, breaking out of the for loop. If you want to return several value, you should return a pointer on an int array containing all the converted values.

Nope, you can't do that... C does not know how to return an array.

Code:

int test( void )
 { 
    int array[10];

    // other stuff

   return array; 
}

This fails because the array is destroyed (goes out of scope) when the function returns.

Yeah sorry, I guess I didn't expressed my idea in the good way. What I meant was returning an int* :

Code:

#include <stdio.h>
#include <stdlib.h>

#define SIZE 4

int *return_array()
{
    int *ret = malloc(SIZE*sizeof(int));
    ret[0]=0;
    ret[1]=1;
    ret[2]=2;
    ret[3]=3;
   
    return ret;
}


int main()
{

    int i;
    int *test = return_array();

    for( i = 0; i < SIZE; i++ )
    {
        printf("%d\n", test[i]);
    }
    
    free(test);    

    return 0;
}

I guess that's good right?

Please slow down. I haven't yet reached till pointers. I thought I understood when Tibo said value will be returned once For loop is broken?

Originally Posted by alter.ego

Please slow down. I haven't yet reached till pointers. I thought I understood when Tibo said value will be returned once For loop is broken?

Sorry if I made things too complicated. Then if you don't know how to use pointer yet, I guess your only solution would be to have an "attoi" function taking one char as paramter, and returning only one int, and call it for every char in you array, maybe storing the returned values in an int array.

Originally Posted by Tibo-88

Yeah sorry, I guess I didn't expressed my idea in the good way. What I meant was returning an int* :

Code:

#include <stdio.h>
#include <stdlib.h>

#define SIZE 4

int *return_array()
{
    int *ret = malloc(SIZE*sizeof(int));
    ret[0]=0;
    ret[1]=1;
    ret[2]=2;
    ret[3]=3;
   
    return ret;
}


int main()
{

    int i;
    int *test = return_array();

    for( i = 0; i < SIZE; i++ )
    {
        printf("%d\n", test[i]);
    }
    
    free(test);    

    return 0;
}

I guess that's good right?

That's better. Even easier since he's handing it the array pointer in the function call would be to alter the array directly.

Thanks for taking out time for the explanation.

At this moment I don't want to return multiple value. I am just intrigued why multiple value isn't getting returned. As per my understanding since output is 6 (which is the numerical equivalent of last element of the array) I am making myself understand that last value is only returned after the for is broken? Any flaw in this logic?

Originally Posted by alter.ego

Thanks for taking out time for the explanation.

At this moment I don't want to return multiple value. I am just intrigued why multiple value isn't getting returned. As per my understanding since output is 6 (which is the numerical equivalent of last element of the array) I am making myself understand that last value is only returned after the for is broken? Any flaw in this logic?

Ok you need to understand how functions work...

Call function .................................................. ........... I'm over here now
.................................................. ..............................Running the function
.................................................. ..............................call return
The function is over
I'm back here now continuing
the program.


Get it? return terminates the function and the program continues from the next step after the function call.
It's over... function done.
You will not get multiple returns because the first time it sees return... the function exits.

Close enough.

Thanks !