Function to return a pointer to the largest number in an array

Question

as you can tell by the title I need to write a function that returns a pointer to the largest number in an array, the functions gets a pointer to a double array and it's size. In addition I need to write a main function that will use this function. Here is the code that I wrote:

#include <stdio.h>
#include <stdlib.h>
void BigEl(double* arr, double arrSize);

void BigEl(double* arr, double arrSize)
{
    int i;
    double  maximum, *x;
    maximum = arr[0];
    for (i = 1; i < arrSize; i++)
    {
        if (arr[i]>maximum)
        {
            maximum = arr[i];
        }
    }
    *x = maximum;
}
void main()
{
    double myarr[10];
    int i;
    printf("Please insert 10 numbers to the array\n");
    for (i = 0; i < 10; i++)
    {
        scanf("%d", &myarr[i]);
    }
    BigEl(myarr, 10);


}

I get this error:

Error   1   error C4700: uninitialized local variable 'x' used

I don't understand what I did wrong because I did initialized x. Any kind of help is appreciated, in addition, tell me if the idea of my code was right because Im not sure if I understood the question correctly.

@haccks whilst true, that's not what's generating the compiler error (which is OP's question). — abligh
– abligh, Commented Mar 28, 2015 at 13:23
@abligh; I didn't say that. My comment was in response to the title. — haccks
– haccks, Commented Mar 28, 2015 at 13:24

abligh · Accepted Answer · 2015-03-28 13:36:11Z

4

You did not initialize the variable x. You merely wrote to the the location pointed to by x, here:

    *x = maximum;

when x was uninitialized, which is what the compiler is complaining about.

You want something like:

double *
BigEl(double* arr, size_t arrSize)
{
    size_t i;
    double *max = arr;
    for (i = 1; i < arrSize; i++)
        if (arr[i] > *max)
            max = &arr[i];
    return max;
}

Things I've changed:

Use size_t for the array size and the counter, not a double and an int.
Retain a pointer to the maximum element, not the maximum element's value.
Return the pointer to the maximum element.
Remove superflous braces.

edited Mar 28, 2015 at 13:36

answered Mar 28, 2015 at 13:22

abligh

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Comments

jensa · Accepted Answer · 2015-03-28 15:08:44Z

2

You're not returning anything. Also, it might be good to take into consideration the case when the array size is 0. Moreover, the size should be passed as a constant. No other answer has mentioned this.

double* BigEl(double* arr, const size_t iSize)
{
    if(iSize == 0)
        return 0;

    double max = arr[0], *x = &arr[0];
    for(unsigned int i=1;i<iSize;++i){
        if(arr[i] > max){
            max = arr[i];
            x = &arr[i];
        }
    }
    return x;
}

edited Mar 28, 2015 at 15:08

answered Mar 28, 2015 at 13:30

jensa

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1 Comment

alk Over a year ago

For completeness it should be mentioned that for array indices the type size_t is the preferred one. Your code will still fail for negative "sizes".

Tom Fenech · Accepted Answer · 2015-03-28 13:30:49Z

Your assignment to *x is incorrect - you are saying "assign to the location pointed to by x, without first saying where that is. Aside from that, there are a couple of other issues:

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

// return pointer to location from function
double * BigEl(double* arr, double arrSize)
{
    int i;
    // initialise both variables
    double maximum = arr[0], *max_pos = arr;

    for (i = 1; i < arrSize; i++)
    {
        if (arr[i]>maximum)
    {
        maximum = arr[i];
        // assign address here
        max_pos = &arr[i];
        }
    }
    // return address
    return max_pos;
}

int main()
{
    double myarr[10];
    double * max_pos;
    int i;
    printf("Please insert 10 numbers to the array\n");
    for (i = 0; i < 10; i++)
    {
        scanf("%lf", &myarr[i]);
    }
    // use return value here
    max_pos = BigEl(myarr, 10);

    return 0;
}

BLUEPIXY · Accepted Answer · 2015-03-28 13:32:03Z

1

//function that returns a pointer to the largest number
double *BigEl(double* arr, int arrSize)
{
    int i;
    double  *maximum;
    maximum = &arr[0];
    for (i = 1; i < arrSize; i++)
    {
        if (arr[i] > *maximum)
        {
            maximum = &arr[i];
        }
    }
    return maximum;
}
int main(void)
{
    double myarr[10];
    int i;
    printf("Please insert 10 numbers to the array\n");
    for (i = 0; i < 10; i++)
    {
        scanf("%lf", &myarr[i]);
    }
    printf("%f\n", *BigEl(myarr, 10));

    return 0;    
}

edited Mar 28, 2015 at 13:32

answered Mar 28, 2015 at 13:26

BLUEPIXY

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Comments

Vlad from Moscow · Accepted Answer · 2015-03-28 13:55:23Z

0

I need to write a function that returns a pointer to the largest number in an array

I think you need the follwoing

#include <stdio.h>

double * largest_element( const double *a, int n )
{
    const double *largest = a;
    int i;

    for ( i = 1; i < n; i++ )
    {
        if ( *largest < a[i] ) largest = a + i;
    }

    return ( double *)largest;

}

#define N   10

int main(void) 
{
    double a[N];
    int i;

    printf("Please insert %d numbers to the array: ", N );

    for ( i = 0; i < N; i++ )
    {
        scanf( "%lf", &a[i] );
    }

    printf( "\nThe largest element of the array is %lf\n", *largest_element( a, N ) );

    return 0;
}

If to enter for example

2.2 1.5 5.2 1.8 3.9 5.9 7.7 6.8 2.9 0.8

then the program output will be

The largest element of the array is 7.700000

answered Mar 28, 2015 at 13:55

Vlad from Moscow

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3 Comments

Vlad from Moscow Over a year ago

@Amnon Hanuhov What do you mean?!

Amnon Hanuhov Over a year ago

I enter like 4 numbers and it finishes the scan, it is suppose to scan 10 times, however if I enter integers it scans 10 times. plus it prints a weird number.

Amnon Hanuhov Over a year ago

Never mind it works, I did a small mistake that I did not notice.

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