Comparing in Array

Question

There is something wrong with my code. I am teaching myself c# and one of the challenges in this chapter was to prompt the user for 10 numbers, store them in an array, than ask for 1 additional number. Then the program would say whether the additional number matched one of the numbers in the array. Now what I have below does work, but only if I enter in a comparison number that is less than 10 which is the size of the array.

I'm not sure how to fix it. I am not sure how to do the comparison. I tried a FOR loop first which kind of worked, but ran through the loop and displayed the comparison against all 10 numbers so you would get 9 lines of No! and 1 line of Yes!. I put in a break; which stopped it counting all 10 but if I entered the number 5 for comparison, then I would get 4 lines of No! and 1 of Yes!. The below has been the only way I could get it to work reliably but only as long as the number isn't out of the bounds of the array.

I can see why I get the error when the number is above 10, I just don't know what to use to compare it but still allow the user to enter in any valid integer. Any assistance would be great!

        int[] myNum = new int[10];
        Console.WriteLine("Starting program ...");
        Console.WriteLine("Please enter 10 numbers.");

        for (int i = 0; i <= 9; ++i)
        {
            Console.Write("Number {0}: ", i + 1);
            myNum[i] = Int32.Parse(Console.ReadLine());
        }

        Console.WriteLine("Thank you.  You entered the numbers ");
        foreach (int i in myNum)
        {
            Console.Write("{0} ", i);
        }

        Console.WriteLine("");
        Console.Write("Please enter 1 additional number: ");
        int myChoice = Int32.Parse(Console.ReadLine());
        Console.WriteLine("Thank you.  You entered the number {0}.", myChoice);

        int compareArray = myNum[myChoice - 1];

        if (compareArray == myChoice)
        {
            Console.WriteLine("Yes!  The number {0} is equal to one of the numbers you previously entered.", myChoice);
        }
        else
        {
            Console.WriteLine("No!  The number {0} is not equal to any of the entered numbers.", myChoice);
        }

        Console.WriteLine("End program ...");

        Console.ReadLine();

Japple · Accepted Answer · 2012-06-14 02:39:30Z

4

You were on the right track- you want to loop through the array in myNum and compare each element to the variable myChoice. If you don't want to print whether each element of the array is a match, create a new variable and use it to keep track of whether you've found a match or not. Then after the loop you can check that variable and print your finding. You'd usually use a bool variable for that- set it false to start, then true when you find a match.

bool foundMatch = false;
for (int i = 0; i < 10; i++) {
    if (myNum[i] == myChoice) {
        foundMatch = true;
    }
}
if (foundMatch) {
    Console.WriteLine("Yes!  The number {0} is equal to one of the numbers you previously entered.", myChoice);
}

answered Jun 14, 2012 at 2:39

Japple

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Jon Senchyna · Accepted Answer · 2012-06-14 03:11:26Z

3

If you include the System.Linq namespace (or if you change the type of myNum to be something that implements ICollection<T>, like List<T>), you can use myNum.Contains(myChoice) to see if the value myChoice matches one of the values in myNum. array.Contains returns a boolean that is true if the specified value is found in the array and false if it is not.

You can update your code to use this like so:

   //int compareArray = myNum[myChoice - 1]; // This line is no longer needed

    if (myNum.Contains(myChoice))
    {
        Console.WriteLine("Yes!  The number {0} is equal to one of the numbers you previously entered.", myChoice);
    }
    else
    {
        Console.WriteLine("No!  The number {0} is not equal to any of the entered numbers.", myChoice);
    }

edited Jun 14, 2012 at 3:11

answered Jun 14, 2012 at 2:36

Jon Senchyna

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2 Comments

CodingWithSpike Over a year ago

Note that the .Contains() method will not compile unless you also have using System.Linq; in your .cs file. It is an "extension method" provided by Linq, and not a method on the array class.

Trido Over a year ago

Using System.Linq; is included by default when I create a new C# Console App. This worked really well. So very very simple.

Patch · Accepted Answer · 2012-06-14 02:31:42Z

1

If you're looking for numbers that are definitely between 1 and 10, then before you use

int compareArray = myNum[myChoice - 1];

check if it's over the value of 10. For example:

while(myChoice > 10)
{
    Console.Write("Please choose a number less than or equal to 10: ");
    myChoice = Int32.Parse(Console.ReadLine());
}

The benefit of putting it inside a while loop instead of an if tag means that, when the user enters another number, the value of myChoice will be rewritten, and compared against. If they enter a number over 10, it'll keep responding Please choose a number less than or equal to 10. until the number they input is below or equal to 10:` Then, your program will continue.

However, if you want to compare it against the array, rather than put in a fixed number comparison, consider the following while loop:

while(myChoice > myNum.Length)
{
    Console.Write("Please choose a number less than or equal to {0}: ", myNum.Length);
    myChoice = Int32.Parse(Console.ReadLine());
}

This will work for any sized array then, without you having to change the while loops content. By using this system, you can then ensure that you won't get an IndexOutOfBounds exception, so long as you subtract 1 when using it as an index.

answered Jun 14, 2012 at 2:31

Patch

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2 Comments

Robotnik Over a year ago

The only problem with the first part is that in the original problem the array holds a list of 10 arbitrary numbers (not specifically the numbers 1-10).

Patch Over a year ago

I realize, but he was trying to run the input as an index. This solves the IndexOutOfBoundsexception.

Brendan Lesniak · Accepted Answer · 2012-06-14 02:42:34Z

0

You are looking to compare a final, 11th value and trying to determine if its in an array of 10 previous entries?

Try:

for(int i = 0; i < array.length - 1; i++;)
{
    If(array[i] == input)
        return true;
}

 return false;

You should be able to figure out how to implement this completely yourself, as you did want to do it as an exercise.

Edit: If someone wants to check this or complete it in correct syntax, go ahead. I posted this rough outline from a phone.

answered Jun 14, 2012 at 2:42

Brendan Lesniak

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