What is the purpose of the following function

Question

This is my task. I googling for find out reason behind this function but can not find out. My teacher tell me what is the use of this function.

My Question is:

What is the purpose of the following function, assuming that the parameter size represents the size of the array data that's also passed as a parameter. Further assume that size is at least 2.

This is sample code he give me:

#include <stdio.h>

void procArray( int data[], int size ) {
     int temp = data[0];
     int index;
     for( index = 0; index < size - 1; index++ )
     {
         data[index] = data[index + 1];
         data[size-1] = temp;
         
         printf("%d ", + data[index]);
         printf("%d ", + data[size-1]);
     }
}

int main()
{
    int arr[2];
    procArray(arr, 2);

    return 0;
}

Every time i got random number in output like:

32767 -2102338448 

Answer 1

The routine procArray appears to be written with the intent that it “rotate” the array one position “left,” meaning to modify the array such that, upon return from the function:

• The last element (index [size-1]) contains the value the first element (index [0]) the first element had upon calling the function.
• Each other element (index [i] for some i other than size-1) contains the value the element to its “right” (index [i+1]) had upon calling the function.

However, if this was the purpose, the function was written incorrectly. The statement data[size-1] = temp; should be after the loop, not inside it.

Further, the main routine fails to demonstrate how the function behaves because it fails to put values into arr.

A corrected function with a useful demonstration is:

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


void procArray(int data[], size_t size)
{
     int temp = data[0];

     for (size_t i = 0; i < size-1; ++i)
         data[i] = data[i+1];

     data[size-1] = temp;
}


int main(void)
{
    int arr[5] = {10, 11, 12, 13, 14};
    procArray(arr, 5);
    for (int i = 0; i < 5; ++i)
        printf("arr[%d] = %d.\n", i, arr[i]);

    return 0;
}

This program outputs:

arr[0] = 11.
arr[1] = 12.
arr[2] = 13.
arr[3] = 14.
arr[4] = 10.

Answer 2

It's because you array is not initialized.

In C, when you write int arr[2] your array is initialized with random value.

Your array doesn't have data in it, so the compiler doesn't know and set a random value.