Recursive function for array integers

Question

I have a function that takes an array a[] and its length n. I must calculate the sum of the numbers inside the array. I wrote this recursive function:

int somma(int a[], int n)
{
 if (n == 0) { return 0; }
 else {return a[n] + somma(a, n-1);}    
}

And I call it in my main() in this way:

int main() {   

 int array[5], ris;

 printf("Type the numbers of the array: \n");

 for(int i=0; i<4; i++)
 { 
   scanf("%d", &array[i]); 
 }

 printf("\nThe sum is: %d.", somma(array,4));

 getch();
 return 0;
}

If the array contains array = [2; 4; 7; 5] the printf must show 18 (2+4+7+5). By the way the function returns me 88, can you help me?

I am using wxDevC++.

Don't forget that a[0] is also an element of the array, which somma skips. — Kninnug
– Kninnug, Commented Oct 26, 2013 at 14:03

digital_revenant · Accepted Answer · 2013-10-26 14:03:06Z

1

You are only reading the first four values in the array. array[4] contains garbage value

for(int i=0; i<5; i++) //change to 5
{ 
     scanf("%d", &array[i]); 
}

Your somma function is also wrong. It will always add 0 for arr[0].

 if (n == -1) { return 0; } //change to this

answered Oct 26, 2013 at 14:03

digital_revenant

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Comments

Rahul Tripathi · Accepted Answer · 2013-10-26 14:04:06Z

1

You may try this:-

for(int i=0; i<=4; i++)
 { 
   scanf("%d", &array[i]); 
 }

Also correct your somma

 if (n == -1) 
 { 
    return 0; 
 }

answered Oct 26, 2013 at 14:04

Rahul Tripathi

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Comments

Stefano Sanfilippo · Accepted Answer · 2013-10-26 14:10:36Z

1

If an array has n elements, then the last element has index n-1. Correct your somma function like this:

int somma(int a[], int n) {
    if (n <= 0) { 
        return 0;
    }

    return a[n-1] + somma(a, n-1);    
}

Additionally, there are two (minor) issues with your code:

Variable declaration inside for head in for(int i=0; i<4; i++) is not allowed by C89, only C99 and C++. Probably DevC++ compiles it because the file is treated as C++, but you should know that it won't compile on GCC, unless you use the -std=c99 switch.
getch is Windows-specific. On POSIX systems, use getchar instead.

edited Oct 26, 2013 at 14:10

answered Oct 26, 2013 at 14:05

Stefano Sanfilippo

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2 Comments

Stefano Sanfilippo Over a year ago

Yes, you are right. I have updated the exit condition for recursion.

Stefano Sanfilippo Over a year ago

Note that the <= it's not strictly necessary (== would be ok), but it will avoid an infinite recursion in case of negative n.

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