How do you get the index number of an array rather than the element?

Question

I have written a basic program to find the largest number in an array and print it:

#include <stdio.h>

int main(void)
{
    int numbers[] = {3, 5, 12, 1, 4};
    int largest;

    largest = numbers[0];

    for (int i = 0; i < sizeof(numbers) / sizeof(numbers[0]); i++)
    {
        if (largest < numbers[i])
        {
            largest = numbers[i];
        }
    }

    printf("The largest number in the array is %i\n", largest);
}

What would I need to do so that instead of printing The largest number in the array is 12, it prints The largest number in the array is numbers[2]?

Keep track of the index. eg if( largest < numbers[i]) { max_index = i; ... } — William Pursell
– William Pursell, Commented Feb 3, 2021 at 21:17
Instead of saving the numbers[i] in the largest variable, just save the i index and then print it. printf("the largest number is numbers[%d]\n", largest); — Marcell Juhász
– Marcell Juhász, Commented Feb 3, 2021 at 21:18

chqrlie · Accepted Answer · 2021-02-03 21:18:43Z

4

Instead of using the value, you would use the index:

#include <stdio.h>

int main(void)
{
    int numbers[] = { 3, 5, 12, 1, 4 };
    int largest;

    largest = 0;

    for (int i = 1; i < sizeof(numbers) / sizeof(numbers[0]); i++)
    {
        if (numbers[largest] < numbers[i])
        {
            largest = i;
        }
    }

    printf("The largest number in the array is numbers[%d]\n", largest);
    return 0;
}

answered Feb 3, 2021 at 21:18

chqrlie

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Comments

Paul Bob · Accepted Answer · 2021-02-03 21:18:55Z

0

One way of doing it is tracking the index

#include <stdio.h>

int main(void)
{
    int numbers[] = {3, 5, 12, 1, 4};
    int largest;
    int index = 0;

    largest = numbers[0];

    for (int i = 0; i < sizeof(numbers) / sizeof(numbers[0]); i++)
    {
        if (largest < numbers[i])
        {
            largest = numbers[i];
            index   = i;
        }
    }

    printf("The largest number in the array is %d at numbers[%d]\n", largest,index);
    return 0;
}

answered Feb 3, 2021 at 21:18

Paul Bob

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Comments

William Pursell · Accepted Answer · 2021-02-03 21:23:34Z

0

I would do something like:

#include <stdio.h>

int
main(void)
{
        int numbers[] = {3, 5, 12, 1, 4};
        int *largest = numbers;
        int *end = numbers + sizeof numbers / sizeof *numbers;

        for(int *s = numbers; s < end; s++ ){
                if( *s > *largest) {
                        largest = s;
                }
        }
        printf("The largest number in the array is %d, at position %td\n",
                 *largest, largest - numbers);
}

answered Feb 3, 2021 at 21:23

William Pursell

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2 Comments

Paul Bob Over a year ago

I don't thhink OP have pointers knowledge, anyway, interesting way to caluculate that index!

M.M Over a year ago

IMO it just adds obfuscation to change from using the index to using a pointer

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