adding two arrays in C

Question

The problem is basically printing two arrays on an external array as right part and left part but although I can print one part, I can not print the other part. The scenario is that for example 5 elements on the left and 7 at the right. Then it reverses the right side and sticks it to the beginning of the array.

Here is the piece of code that I typed.

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

int main()
{
 int mainarray[] = {} , n , i , rank;

 printf("\nHow many element[10..2000]: ");
 scanf("%d", &n);
 printf("\nEnter the array elements : ");
 for(i=0; i<n; ++i)
 {
      scanf("%d" , &mainarray[i]);
 }
 printf("\nThe array is : ");
 for(i=0 ; i<n ; i++)
 {
     printf("%d ",mainarray[i]);
 }    
 printf("\n\nEnter the rank of the element : ");
 scanf("%d",&rank);
 printf("\n\nElement on rank %d is: %d",rank, mainarray[rank-1]);


 int leftarray[] = {} , rightarray[] = {};

 for(i=0; i<=rank ; i++)
 {
          leftarray[i] = mainarray[i];
 }
 printf("\n\nThe left array is : ");
 for(i=0 ; i<=rank ; i++)
 {
         printf("%d ", leftarray[i]);
 }

 for(i=0 ; i<n-rank-1 ;i++)
 {
              rightarray[i]=mainarray[i+rank+1];
 }
 printf("\n\nThe right array is : ");
 for(i=0 ; i<n-rank-1 ;i++)
 {
         printf("%d ", rightarray[i]);
 }

 int j=n-rank-2,temp;
 i=0;
 while(i<j)
 {
           temp=rightarray[i];
           rightarray[i]=rightarray[j];
           rightarray[j]=temp;
           i++;
           j--;
 }
 printf("\n\nNew right array is : ");
 for(i=0 ; i<n-rank-1 ; i++)
 {
         printf("%d ", rightarray[i]);
 }

 i=0;

 while(i<n-rank-1)
 {
                mainarray[i]=rightarray[i];
                i++;
 }
 j=0;
 while(j<rank+1 && i<n-1)
 {
           mainarray[i]=leftarray[j];
           j++;
           i++;
 }

 printf("\n\nThe result is : ");
 for(i=0 ; i<n ; i++)
 {
         printf("%d ",mainarray[i]);
 }    

 printf("\n\n\n");
 system("pause");
 return 0;
}

int mainarray[] = {} - ouch. if you were shooting for an array that can hold no elements, you found it. — WhozCraig
– WhozCraig, Commented Oct 28, 2016 at 16:37
When you do int mainarray[] = {} you define mainarrayas an empty array. All indexing of it will be out of bounds. — Some programmer dude
– Some programmer dude, Commented Oct 28, 2016 at 16:37
How can I create an array without declaring the size? @Someprogrammerdude — erengsgs
– erengsgs, Commented Oct 28, 2016 at 16:43

Barmar · Accepted Answer · 2016-10-28 16:41:14Z

1

You're declaring empty arrays when you write:

int mainarray[] = {};

As a result, you're storing outside the array bounds, which results in undefined behavior.

You need to declare the arrays after you get the size from the user.

scanf("%d", &n);
int mainarray[n]; // no need to initialize here, you're going to fill it in with the input loop

Then do similar things for leftarray and rightarray:

scanf("%d",&rank);
int leftarray[rank];
int rightarray[n-rank];

answered Oct 28, 2016 at 16:41

Barmar

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1 Comment

erengsgs Over a year ago

Thank you so much @Barmar the problem will be solved after some tiny changes.

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