Finding Minimum Value in Recursive Arrays

thulaotzu · #1 16-Nov-2005, 22:11

I have an assignment that asks me to find the minimum value in an array.

Here are the instructions given by my instructor:
Write a C++ program having a recursive function recursiveMinimum that takes an integer array and the array size as arguments and returns the smallest element of the array. The function should stop processing and return when it receives an array of 1 element.

I got the program to sort the elements from smallest to largest, but I believe my code contains logical errors. I'm having trouble with the latter part of the assignment. The part that says... "The function should stop processing and return when it receives an array of 1 element". Can someone help me with this situation?

Here is my written code:

CPP / C++ / C Code:

 
#include <iostream>

using std::cout;
using std::endl;

#include <iomanip>

using std::setw;


int main ()
{


void recursiveMinimum (int);	
	
	
	const int arraySize = 13; // size of array a
	int a[ arraySize ] = { 10, 55, 77, 3, 8, 54, 22, 11, 16, 18, 100, 25, 29 };
	int hold; // temporary location used to swap array elements
	int e;

	cout << "Data items in original order:\n";

	// output original array
	for ( int i=0; i < arraySize; i++ )
		cout << setw(4) << a[i];

	// bubble sort
	// loop to control number of passes
	for ( int pass = 0; pass < arraySize - 1; pass++ )
			
		// loop to control number of comparisons per pass
		for ( int j = 0; j < arraySize - 1; j++ )

			// compare side-by-side elements and swap them if 
			// first element is greater than second element
			if ( a[j] > a[j + 1] ) {
				hold = a [j];
				a [j] = a [j + 1];
				a [j +1] = hold;

			} // end if

		
		cout << endl << "The data items in sorted order is: \n";
		// output sorted array
		for (int k=0; k < arraySize; k++ )
			cout << setw(4) << a[k];

				
		recursiveMinimum ( a[0]);
		cout << endl << endl << "The smallest element of the array is: ";
		cout << a[0] << endl << endl;

				
		
		return 0;	// indicates sucessful termination
}

void recursiveMinimum (int e)
{
    
	 e *= 1;

} // end main

WaltP · #2 16-Nov-2005, 23:54

Quote:

Originally Posted by thulaotzu

Here are the instructions given by my instructor:
Write a C++ program having a recursive function recursiveMinimum that takes an integer array and the array size as arguments and returns the smallest element of the array. The function should stop processing and return when it receives an array of 1 element.

I got the program to sort the elements from smallest to largest, but I believe my code contains logical errors.

Your logic problem is sorting the array. Nowhere in the instructions does it say sort. You need to simply create a function that recursively tests the array elements and returns the lowest value.

Based on my interpretation of the instructions, the function accepts the array and a size. Use the size as an index into the array to test the last element. You can then subtract one from the size and call the function again. When the size gets to one, you start the return phase of the recursion...

thulaotzu · #3 17-Nov-2005, 04:55

Do you think I shoud ask the user to input numbers?

For example,

CPP / C++ / C Code:

 int numbers [20];

cout << "Enter 20 numbers";
cin >> numbers;

Is that how we should approach the program?.

WaltP · #4 17-Nov-2005, 12:31

Quote:

Originally Posted by thulaotzu

Do you think I shoud ask the user to input numbers?

Has no bearing on the problem. Get the information in the array any way you want. At first

CPP / C++ / C Code:

int numbers[6] = { 23, 41, 2, 14, 56, 8};

would be adequate.
Once you have the program running, switch to input.

kobi_hikri · #5 17-Nov-2005, 14:35

Please notice that you where given a clue about the function prototype ...
The function gets the array and the array size and returns the minimal value. You used void function, so you do not comply to all of the instructions.

try something like :

CPP / C++ / C Code:

int recursiveMinimum(int my_array[],unsigned array_size);

And keep in mind that your function should stop when the array size is 1 (still, you need to check that last argument - don't forget it), so your recursive calls will decrement the array size value along your algorithm.

Keep us posted,
Kobi.

thulaotzu · #6 18-Nov-2005, 01:06

In the function:

CPP / C++ / C Code:

int recursiveMinimum(int my_array[],unsigned array_size);

Why is array_size "unsigned"?.. Can someone explain why it's unsigned?

Also, how can I compare the elements so that I can display the smallest element of the array?

WaltP · #7 18-Nov-2005, 01:59

Quote:

Originally Posted by thulaotzu

In the function:

CPP / C++ / C Code:

int recursiveMinimum(int my_array[],unsigned array_size);

Why is array_size "unsigned"?.. Can someone explain why it's unsigned?

Short answer -- because that's how Kobi defined it.
Long answer -- Why not? Can the size of an array be negative? It doesn't have to be unsigned, but it doesn't hurt.

Quote:

Originally Posted by thulaotzu

Also, how can I compare the elements so that I can display the smallest element of the array?

Essentially, as the instructions state, you return when the array size becomes 1. You return the current array element (which is the 1st element). This becomes the initial guess at the minimum value.

This continues the previous instance of the function (array size == 2). Compare the returned value with the current (2nd) element. return the lower of the two values.

Continue....

kobi_hikri · #8 18-Nov-2005, 02:21

Quote:

Originally Posted by thulaotzu

Why is array_size "unsigned"?.. Can someone explain why it's unsigned?

1. Because the index of an array >=0.
If you get used to passing the "logical" argument, then you may be warned by the compiler about possible logical errors (I'm using VC6 with warning level 4).
2. Because I think this is the correct way to define the requested function.

About your other question : Comparing the elements. I see Walt answered you and I can only suggest you look at recursion examples.
Post the code you wrote untill now.

Best regards,
Kobi.

thulaotzu · #9 18-Nov-2005, 07:39

I'm almost at the point where I can begin the program.. I'm still stuck on something. For example, the following..

Quote:

Originally Posted by WaltP

Has no bearing on the problem. Get the information in the array any way you want. At first

CPP / C++ / C Code:

int numbers[6] = { 23, 41, 2, 14, 56, 8};

would be adequate.
Once you have the program running, switch to input.

I'm not sure how to "switch to input".. Can someone show me how I would do this?

Also, how many for loops would I need in this program?

Paramesh · #10 18-Nov-2005, 07:47

Thu, you misunderstood what Walt meant.
He meant that, for testing, go with the sample array with size 6.

Once you have successfully created the recursion function, and verified the results, you can get the input from the user.

So, dont worry about input for now...

Quote:

Originally Posted by Thu

Also, how many for loops would I need in this program?

That depends on how you write the program. This is irrelevant.

Anyway, Here is how you get the input for the array: (go with the sample array for testing...)

For that, get the the input from the user about what is the size of the array.
then create the array using the new operator.
Get the input using a loop and a cin statement.

Here is one example:

CPP / C++ / C Code:

int size;

cout<<"Enter the size of the array..";
cin >> size;

int numbers[] = new int[size];

cout<<"Enter the numbers one by one.." << endl;

for( int i = 0; i < size; i++ )
{
   cin >> numbers[i];
}

After doing this, the numbers will be stored in the array.

Regards,
Paramesh.

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