Thread: help with sorting numbers

I have this program I've been working on in this c book I have and it wants me to sort numbers in ascending or descending order I think I can figure out the descending anyway I know that I might have to use an if statement but maybe not I have this worksheet from when I took c# that has the code to sort in descending order so I think I can figure that out here is my lame attempt it doesn't sort I'm trying to well I know what it does it just prints 10 10 times I know I have to compare the array 0 with array 1 then which ever is bigger then print that first I think but I can't figure out what to do heres my code

Code:

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

void SortAscending(void);
void SortDescending(void);

int iArray[9];
int x;


int main()
{


	int iChoice = 0;
	
	for (x = 0; x < 10; x++)
	{
	printf("\n\tEnter ten numbers: ");
	scanf("%d",&iArray[x]);
	}

	system("cls");

	printf("\n\tEnter sorting method\n");
	printf("1\tAscending order\n");
	printf("2\tDescending order\n");
	printf("Enter number: ");
	scanf("%d",&iChoice);

	if (iChoice == 1)
		SortAscending();
	else if(iChoice == 2)
		SortDescending();



}

void SortAscending()
{
	for(x = 0; x < 10; x++)
		if (iArray[x] >= iArray[x]+x)
			printf("%d\n",iArray[x]);
		else
			printf("%d\n",iArray[x]+x);

	
}

void SortDescending()
{
}

Hey,

There are some issues with your code and I would recommend to also read a book about algorithms, especially sorting algorithms, because that what you do has nothing to do with sorting an array ... Please find some of the comments to your code below.

Originally Posted by artistunknown

Code:

       int iArray[9];
       ...
	for (x = 0; x < 10; x++)
	{
	printf("\n\tEnter ten numbers: ");
	scanf("%d",&iArray[x]);
	}

You create an array with 9 elements, but you finally write 10 elements into it. Your app might not crash immediately, but you should not do that ...

Originally Posted by artistunknown

Code:

system("cls");

The use of the system(3) library call is very system-dependent. IIRC, "cls" is a Windows command, but it is not available on Linux. Though, your code isn't really portable. For hints, you might want to read this FAQ: Cprogramming.com FAQ > Clear the screen?

Originally Posted by artistunknown

Code:

void SortAscending()
{
	for(x = 0; x < 10; x++)
		if (iArray[x] >= iArray[x]+x)
			printf("%d\n",iArray[x]);
		else
			printf("%d\n",iArray[x]+x);

	
}

As I already said above, that is NOT sorting. Assume you have an array of 3 with the following values: [5 - 10 - 1]. You will never get the 1 at the first position assuming ascending order.

Here are some sorting algorithms which you could look up in the web:

• Bubble sort
• Merge sort
• Quick sort
• Insertion sort
• Sorting algorithm - Wikipedia, the free encyclopedia

- Andi -

Code:

void SortAscending()
{
	for(x = 0; x < 10; x++)
		if (iArray[x] >= iArray[x]+x)
			printf("%d\n",iArray[x]);
		else
			printf("%d\n",iArray[x]+x);

	
}

Make your array size 10 (or whatever number), and then use x < 10. 
Here you made your array size only 9, so in C with zero based arrays, 
your x variable will run beyond the top of the array on the last loop.

You need two nested loops to sort a 1D array. something like this:

for(i = 0; i < 9-1; i++) {
  for(j = i+1; j < 9; j++) {
     if(a[i] > a[j]) {  //change to < for descending sort, and no = is needed
       temp = a[i];
       a[i] = a[j];
       a[j] = temp;
     }
  }
}

Change the 9 to 10 if you change the array size to 10, in for loops.

That will get your sorts going, although this is a slow sorter on large arrays.

hey thanks guys I guess learning sorting algorithms is in data structures classes and I'm not that advanced yet but I will get a book on data structures I will also read the faqs you suggested

Yeah I have to admit my code was pretty lame this is the finished product from what adak taught me

Code:

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

void SortAscending(void);
void SortDescending(void);

int iArray[9];



int main()
{
	int x;
	int iChoice = 0;
	
	for (x = 0; x < 10; x++)
	{
	printf("\n\tEnter ten numbers: ");
	scanf("%d",&iArray[x]);
	}

	system("cls");

	printf("\n\tEnter sorting method\n");
	printf("1\tAscending order\n");
	printf("2\tDescending order\n");
	printf("Enter number: ");
	scanf("%d",&iChoice);

	if (iChoice == 1)
		SortAscending();
	else if(iChoice == 2)
		SortDescending();



}

void SortAscending()
{
	int i;
	int j;
	int temp;

	for(i = 0; i < 10; i++)
	{
		for(j = i+1; j < 10; j++)
		{
			if(iArray[i] > iArray[j])
			{  
				temp = iArray[i];
				iArray[i] = iArray[j];
				iArray[j] = temp;
				
     			}
  		}
		printf("%d\n",iArray[i]);
	}
	
}

void SortDescending()
{
	int i;
	int j;
	int temp;

	for(i = 0; i < 10; i++)
	{
		for(j = i+1; j < 10; j++)
		{
			if(iArray[i] < iArray[j])
			{  
				temp = iArray[i];
				iArray[i] = iArray[j];
				iArray[j] = temp;
				
     			}
  		}
		printf("%d\n",iArray[i]);
	}
}

after I posted I thought maybe I should use a nested loop but I would have never guessed this code yeah I don't know the language good enough

One slight correction to make, ArtistUnknown:

Code:

	for(i = 0; i < 10-1; i++)   //change from < 10 to < 10-1
	{
		for(j = i+1; j < 10; j++)
		{
			if(iArray[i] < iArray[j])
			{  
				temp = iArray[i];
				iArray[i] = iArray[j];
				iArray[j] = temp;
				
     			}
  		}
		printf("%d\n",iArray[i]);
	}

Because j is always one starting one element higher in the array than i. On the last time through the loop, i needs to be one less than the last element to keep j from going outside the top of the array.

ok thanks should i = 1 or i = 0 in that loop when I run the code the way I have it it works but I will change it

hey I ran the code on that it won't print out the last number if I use 10 - 1

oh yeah I think I remember something like that in c# class sorry I know you guys must get bored with answering stupid questions on here

does this look better

Code:

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

void SortAscending(void);
void SortDescending(void);

int iArray[9];



int main()
{
	int x;
	int iChoice = 0;
	
	for (x = 0; x < 10; x++)
	{
	printf("\n\tEnter ten numbers: ");
	scanf("%d",&iArray[x]);
	}

	system("cls");

	printf("\n\tEnter sorting method\n");
	printf("1\tAscending order\n");
	printf("2\tDescending order\n");
	printf("Enter number: ");
	scanf("%d",&iChoice);

	if (iChoice == 1)
		SortAscending();
	else if(iChoice == 2)
		SortDescending();



}

void SortAscending()
{
	int i;
	int j;
	int temp;

	for(i = 0; i < 9; i++)
	{
		for(j = i+1; j < 10; j++)
		{
			if(iArray[i] > iArray[j])
			{  
				temp = iArray[i];
				iArray[i] = iArray[j];
				iArray[j] = temp;
				
     			}
  		}
		printf("%d\n",iArray[i]);
	}
	printf("%d\n",iArray[i]);
}

void SortDescending()
{
	int i;
	int j;
	int temp;

	for(i = 0; i < 9; i++)
	{
		for(j = i+1; j < 10; j++)
		{
			if(iArray[i] < iArray[j])
			{  
				temp = iArray[i];
				iArray[i] = iArray[j];
				iArray[j] = temp;
				
     			}
  		}
		printf("%d\n",iArray[i]);
	}
	printf("%d\n",iArray[i]);
}