450DSA Array in C - arrays

Question

/**
#brief Move all negative elements to end
EX: Given an unsorted array arr[] of size N having both negative and positive integers.
The task is place all negative element at the end of array
without changing the order of positive element and negative element.
Example 1:
Input :
N = 8
arr[] = {1, -1, 3, 2, -7, -5, 11, 6 }
Output :
1 3 2 11 6 -1 -7 -5
Example 2:
Input :
N=8
arr[] = {-5, 7, -3, -4, 9, 10, -1, 11}
Output :
7 9 10 11 -5 -3 -4 -1
*/
#include<stdio.h>
void shortArray(int array[], int stack[]){
int size = 8;
int left = 0;
int right = size;
for(int i=0; i<size; i++){
if(left = right) break;
volatile int value = array[i];
if(array[i] > 0){
stack[left] = value;
left ++;
}
if(array[i] < 0){
stack[right] = value;
right--;
}
}
}
//printarray
void printArray(int array[], int size){
for(int i=0; i<size; i++){
printf(" %d", array[i]);
}
}
int main(){
int array[] = {-5, 7, -3, -4, 9, 10, -1, 11};
int size = 8;
int stack[size];
shortArray(array, stack);
printArray(stack, size);
return 0;
}
my output:
0 0 0 0 0 0 0 0
i try to assign value to stack[] but it don't work right.
i dont know what wrong with it? can you tell me why? thank you!
sorry for my bad english :<

Answer 1

For starters the assignment sounds like
The task is place all negative element at the end of array
It means that you need to change the source array in place not to build a new array.
In this if statement
if(left = right) break;
there is used the assignment operator = instead of the equality operator ==. So if right initially is not equal to 0 then the loop breaks at once.
Using the qualifier volatile in this declaration
volatile int value = array[i];
has no any sense.
If the first element of the source array is negative then this if statement
if(array[i] < 0){
stack[right] = value;
right--;
}
invokes undefined behavior because the index right points to memory after the last element of the array stack.
And moreover with this approach the order of negative values will be broken
And the function shall not use the magic number 8. It should be able to deal with arrays of various sizes. So the function must accept the number of elements in the passed to it array.
The function can be defined for example the following way as it is shown in the demonstration program below
#include <stdio.h>
void partition( int a[], size_t n )
{
for (size_t i = 0, j = 0; i < n; )
{
while (j != n && !( a[j] < 0 )) j++;
if (!( j < i )) i = j;
while (i != n && a[i] < 0) i++;
if (i != n)
{
int tmp = a[i];
for ( size_t k = i; k != j; --k )
{
a[k] = a[k - 1];
}
a[j] = tmp;
i++, j++;
}
}
}
int main( void )
{
int a[] = { 1, -1, 3, 2, -7, -5, 11, 6 };
const size_t N = sizeof( a ) / sizeof( *a );
for (size_t i = 0; i < N; i++)
{
printf( "%d ", a[i] );
}
putchar( '\n' );
partition( a, N );
for (size_t i = 0; i < N; i++)
{
printf( "%d ", a[i] );
}
putchar( '\n' );
}
The program output is
1 -1 3 2 -7 -5 11 6
1 3 2 11 6 -1 -7 -5