C language copying arrays - error in code

Question

I am trying to copy elements from two arrays into a third.
I can't understand why it doesn't work.
I made sure that the two arrays are filled properly, but for some reason, the actual copying doesn't work- when I print the elements of the arr3, I get some random numbers.

#include <stdio.h>

int main()
{
    int arr1[10], arr2[10], arr3[20];
    int i, n;


    printf("Enter a number of elements to be stored in each array (up to 10): ");
    scanf("%d", &n);
    printf("Enter the %d elements to the first array:\n", n);
    for (i = 0; i < n; i++)
    {
        printf("Element %d: ", i + 1);
        scanf("%d", &arr1[i]);
    }
    printf("Enter the %d elements to the second array:\n", n);
    for (i = 0; i < n; i++)
    {
        printf("Element %d: ", i + 1);
        scanf("%d", &arr2[i]);
    }
/*
// A test to make sure first 2 array are filled by the user- works

    for(i = 0; i < n; i++)
        printf("%d  ", arr1[i]);
    for(i = 0; i < n; i++)
        printf("%d  ", arr2[i]);

*/
    // something wrong here, the elements are not coppied to the third array
    for(i = 0; i < n; i++);
            arr3[i] = arr1[i];
    for(i = n; i < 2 * n; i++)
        arr3[i] = arr2[i];


    for(i = 0; i < 2 * n; i++)
        printf("%d\n", arr3[i]);

    return(0);
}

arr3[i]=arr2[i]; : The subscript of arr2 should start from 0. — BLUEPIXY
– BLUEPIXY, Commented Apr 18, 2017 at 14:29
#include <string.h> memcpy(arr3, arr1, n * sizeof(*arr1)); memcpy(arr3 + n, arr2, n * sizeof(*arr2)); — BLUEPIXY
– BLUEPIXY, Commented Apr 18, 2017 at 14:32

cleblanc · Accepted Answer · 2017-04-18 14:46:35Z

3

You're reading past the end of arr2, try this;

for (i = 0; i < n; i++)
        arr3[i] = arr1[i];
for (i = 0; i < n; i++)
    arr3[n+i] = arr2[i];

edited Apr 18, 2017 at 14:46

answered Apr 18, 2017 at 14:19

cleblanc

3,6881 gold badge16 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Hana Over a year ago

Thanks. I understand why your code works, I don't understand why my doesn't. Lets say n=3. when I copy from arr2 I start from arr3[3] and end with arr3[5]. what is it wrong?

cleblanc Over a year ago

arr1 and arr2 have elements 0, 1, and 2. When n is 3. If you first copy arr1[0..2] to arr3[0..2] then you try to copy arr2[3..5] to arr3[3..5] but arr2 doesn't have data there. Do you understand?

Hana Over a year ago

I do now. Thanks. Can't find where you mark the question as resolved..

mudit Panwar · Accepted Answer · 2017-04-18 14:33:21Z

-1

That's because your code is reading arr2[10],arr2[11] ..... arr2[19] (if n=10 ), all these values do not exist because arr2 only has 10 values. you can use this.

for (i=0; i<n; i++)
arr3[n+i]=arr2[i];

or

for (i=n; i<n*2; i++)
arr3[i]=arr2[i-n];

answered Apr 18, 2017 at 14:33

mudit Panwar

573 bronze badges

Collectives™ on Stack Overflow

C language copying arrays - error in code

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related