Thread: Need help on flip array algorithm

Dear Sir or Madam:
I have been struggling in finding a way to flip an array.
I want to flip array from begin index to end index.

Code:

  float  Array[5] = {3.0,  5.7,  6.0,  8.9,  9.4};

  this means:  Array[0] = 3.0
                      Array[1]  = 5.7
                      Array[2]  = 6.0
                      Array[3]  = 8.9
                      Array[4]  = 9.4

How can I flip this array so that it become:

                     Array[4] = 3.0
                     Array[3] = 5.7
                     Array[2] = 6.0
                     Array[1] = 8.9
                     Array[0] = 9.4

If an array is larger such as 1000 elements , how can i flip it by a
special algorithm?
Your help would deeply appreciated.

DiepVien_007

You could do swapping by introducting a temporary variable.

temp = array [i];
array [i] = array [j];
array [j] = temp;

To swap the complete array you would need to let i run from 0 until half of the array. The variable j runs from the last element index until half of the array. Or, you could calculate j by realising that the j should decrease at same speed as i increases.

Hello, well, I don't know if this is a good way to do this, but:

Code:

#include <stdio.h>

#define SIZE 5

int main(void) {
	int i;
	float arr[SIZE] = {3.0, 5.7, 6.0, 8.9, 9.4};
	float tmp;
	
	for (i=0; i<SIZE; ++i)
		printf("arr[%d] = %.1f\n",i,arr[i]);

	//rotate the array, loop until the middle (I think)
	for (i=0; i<(SIZE/2)+1; i++) 
	{
		tmp = arr[i];
		arr[i] = arr[SIZE-i-1];
		arr[SIZE-i-1] = tmp;
	}

	printf("\n\n");
	for (i=0; i<SIZE; ++i)
		printf("arr[%d] = %.1f\n",i,arr[i]);
	return 0;
}