Merging two 1D arrays in C

#include <stdio.h>
#include <conio.h>
#include <malloc.h>
#include <windows.h>
#define MAX1 5
#define MAX2 7
int *arr ;
int* create ( int ) ;
void sort ( int *, int ) ;
void display ( int *, int ) ;
int* merge ( int *, int * ) ;
int main( )
{
 int *a, *b, *c ;
 system ( "cls" ) ;
 printf (  "Enter elements for first array:\n\n" ) ;
 a = create ( MAX1 ) ;
 printf ( "Enter elements for second array:\n\n" ) ;
 b = create ( MAX2 ) ;
 sort ( a, MAX1 ) ;
 sort ( b, MAX2 ) ;
 printf ( "First array:\n" ) ;
 display ( a, MAX1 ) ;
 printf ( "Second array:\n" ) ;
 display ( b, MAX2 ) ;
 printf ( "After Merging:\n" ) ;
 c = merge ( a, b ) ;
 display ( c, MAX1 + MAX2 ) ;
 return 0 ;
}
/* creates array of given size, dynamically */
int* create ( int size )
{
 int *arr, i ;
 arr = ( int * ) malloc ( sizeof ( int ) * size ) ;
 for ( i = 0 ; i < size ; i++ )
 {
  printf ( "Enter the element no. %d: ", i + 1 ) ;
  scanf ( "%d", &arr[i] ) ;
 }
 printf ( "\n" ) ;
 return arr ;
}
/* sorts array in ascending order */
void sort ( int *arr, int size )
{
 int i, temp, j ;
 for ( i = 0 ; i < size ; i++ )
 {
  for ( j = i + 1 ; j < size ; j++ )
  {
   if ( arr[i] > arr[j] )
   {
    temp = arr[i] ;
    arr[i] = arr[j] ;
    arr[j] = temp ;
   }
  }
 }
}
/* displays the contents of array */
void display ( int *arr, int size )
{
 int i ;
 for ( i = 0 ; i < size ; i++)
  printf (  "%d\t", arr[i] ) ;
 printf ( "\n" ) ;
}
/* merges two arrays of different size */
int* merge ( int *a, int *b )
{
 int *arr ;
 int i, k, j ;
 int size = MAX1 + MAX2 ;
 arr = ( int * ) malloc ( sizeof ( int ) * ( size ) ) ;
 for ( k = 0, j = 0, i = 0 ; i <= size ; i++ )
 {
  if ( a[k] < b[j] )
  {
   arr[i] = a[k] ;
   k++ ;
   if ( k >= MAX1 )
   {
    for ( i++ ; j < MAX2 ; j++, i++ )
     arr[i] = b[j] ;
   }
  }
  else
  {
   arr[i] = b[j] ;
   j++ ;
   if ( j >= MAX2 )
   {
    for ( i++ ; k < MAX1 ; k++, i++ )
     arr[i] = a[k] ;
   }
  }
 }
 return arr ;
}