Thread: Inserting into array

This is my sample code , however i seem to get an odd answer , can someone explain why i get my ans as :

This is the Terminal output , LOOK BELOW FOR THE CODE

Enter Element: 1 1

Enter Size of Array:1 4


Enter 4 Elements into the Array:


Enter Element: 1 1


Enter Element: 2 2


Enter Element: 3 3


Enter Element: 4 4


Enter Size of Array:2 4


Enter 4 Elements into the Array:


Enter Element: 1 1


Enter Element: 2 2


Enter Element: 3 3


Enter Element: 4 4


Insert Array:1 into Array:2 at Position: 1


Size of Array :2 is 4
The New array Size 8 :


1
1
2
3
4
2
3
2. <why 2 here IT SHOULD BE 4 ?????

code

Code:

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

int main()
{
  int n, m, key, loc, i;

  system("clear");

  //const int n=10;//n =sizeof(a)/sizeof(int);

  printf("\nEnter Size of Array:1\t");
  scanf("%d", &m);
  int a[m];
  printf("\nEnter %d Elements into the Array:\n", m);
  for (i = 0; i < m; i++) {
    printf("\nEnter Element: %d\t", i + 1);
    scanf("%d", &a);
  }

  printf("\nEnter Size of Array:2\t");
  scanf("%d", &n);
  int b[n];
  printf("\nEnter %d Elements into the Array:\n", n);
  for (i = 0; i < n; i++) {
    printf("\nEnter Element: %d\t", i + 1);
    scanf("%d", &b);
  }

  printf("\nInsert Array:1 into Array:2 at Position:\t ");
  scanf("%d", &loc);

  printf("\nSize of Array :2 is %d", n);

  //shifting
  for (i = m - 1; i >= loc; i--) {
    a[i + n] = a;
  }

  for (i = 0; i < n; i++)       //insert n elements from 2nd array
  {
    a[loc + i] = b;
  }

  n = m + n;
  printf("\nThe New array Size %d :", n);

  for (i = 0; i < n; i++) {
    printf("\n%d", a);
  }

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

> why 2 here IT SHOULD BE 4 ?????
Because an array doesn't get bigger just by assigning values out of bounds.

Code:

  //shifting
  for (i = m - 1; i >= loc; i--) {
    a[i + n] = a;
  }

You need to make another array, which is the new total size.

i don't get it , but what i'm doing is shifting the values by n number then inserting the second array in the space , so what is the issue here ?
//shifting
for(i=m-1;i>=loc;i--)
{
a[i+n] = a[i];
}

for(i=0;i<n;i++) //insert n elements from 2nd array
{
a[loc+i]=b[i];
}

Array a is m elements long. Array b is n elements long.
So neither of them is big enough to hold n + m elements.

You created the arrays to be a certain size.
That is the size they are.
They do not magically change their size just because you try to access memory outside the array bounds.

BTW, I didn't say you had to make a new array. You just need to ensure that the array you insert into has enough space.

Code:

#include <stdio.h>
#include <stdlib.h>
 
int main()
{
    printf("\nEnter Size of Array:1\t");
    int m;
    scanf("%d", &m);
    int a[m];
 
    printf("\nEnter %d Elements into the Array:\n", m);
    for (int i = 0; i < m; i++)
    {
        printf("\nEnter Element: %d\t", i + 1);
        scanf("%d", &a[i]);
    }
    
    printf("\nEnter Size of Array:2\t");
    int n;
    scanf("%d", &n);
    int b[n + m];  // enough size for both
 
    // but we're only using the first n at first
    printf("\nEnter %d Elements into the Array:\n", n);
    for(int i = 0; i < n; i++)
    {
        printf("\nEnter Element: %d\t", i + 1);
        scanf("%d", &b[i]);
    }
 
    printf("\nInsert Array:1 into Array:2 at Position:\t ");
    int loc;
    scanf("%d", &loc);
 
    // ... you should ensure that loc is within range ...
 
    for (int i = n - 1; i >= loc; i--) 
        b[i + m] = b[i];
 
    for (int i = 0; i < m; i++) //insert m elements from 1st array
      b[loc + i] = a[i];
 
    n += m;
    printf("\nThe New array Size %d:\n", n);
 
    for (int i = 0; i < n; i++)
        printf("%d\n", b[i]);
 
    return 0;
}