Declaring variable within 'while loop' but can't change value during loop

Question

I'm trying to make this loop work so it will keep asking for a number until the user enters 999. However with this version of code, it won't build saying I can't declare num within the loop becuase I'm giving it different meaning in this scope.

The try and catch are used because of my assignment rules for this piece of code.

int num;
while (num != 999)
{
    Console.WriteLine("Enter a number between 0 and 99");
    string input = Console.ReadLine();
    try
    {
        int num = Convert.ToInt32(input);
        Console.WriteLine("This is element number " + num + " : " + randNums[num]);
    }
    catch
    {
        Console.WriteLine("Data inputted is not between 0 and 99");
    }
}
Console.WriteLine("You chose the secret value, well done!");

In the 1st line the num variable should be initialized to some value before it can be used. Even if that is not the problem, I think the compiler will complain — Antonio
– Antonio, Commented Feb 25, 2014 at 23:24

p.s.w.g · Accepted Answer · 2014-02-25 23:21:21Z

2

The problem is that you're declaring the variable twice with int num. You don't need to redeclare the variable within the loop, just assign it:

int num = 0; // initialized num to 0 here
while (num != 999)
{
    Console.WriteLine("Enter a number between 0 and 99");
    string input = Console.ReadLine();
    try
    {
        num = Convert.ToInt32(input); // Changed int num to num here
        Console.WriteLine("This is element number " + num + " : " + randNums[num]);
    }
    catch
    {
        Console.WriteLine("Data inputted is not between 0 and 99");
    }
}
Console.WriteLine("You chose the secret value, well done!");

answered Feb 25, 2014 at 23:21

p.s.w.g

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Comments

aw04 · Accepted Answer · 2014-02-25 23:29:26Z

2

You have int num defined twice in the same scope. Change the name of one of them. The one inside the loop is invalid since you already have one defined.

Alternately you can remove int from the inner one if you want to re-assign the same variable. This way it will overwrite it each time with a new value.

Also when you initialize it the first time, be sure to assign it a value.

Example:

int num = 0;

edited Feb 25, 2014 at 23:29

answered Feb 25, 2014 at 23:20

aw04

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6 Comments

Tom Carter Over a year ago

I want them to be the same thing though.

crthompson Over a year ago

@TomCarter, You want them to be the same? I dont understand that. That would seem to indicate that you want num to always be 0.

aw04 Over a year ago

@paqogomez I think he means he wants to reassign it each time through the loop

crthompson Over a year ago

That makes a bit more sense. @TomCarter, if you put int in front of a variable name, you are redeclaring the variable. You dont want to redeclare, you just want to assign the value from input.

crthompson Over a year ago

@Antonio makes a good point in the comments. The first one needs to be set to 0 initially.

|

Selman Genç · Accepted Answer · 2014-02-25 23:43:27Z

1

In addition to other answers, you can do this, for example:

if (someCondition)
{
     int num = 23;
}
else
{
     int num = 12;
}

But you can't do this:

int num = 12;
if(someCondition)
{
   int num = 23;
}

Because all variables has it's own scope, and if you define a variable in outer scope, you can't define a new variable with the same name in the inner-scope.So if you just want to update the value of your variable, you don't need to declare it again, just use a simple assignment.See Compiler Error CS0136 documentation for more details.

edited Feb 25, 2014 at 23:43

answered Feb 25, 2014 at 23:29

Selman Genç

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Comments

McAden · Accepted Answer · 2014-02-25 23:22:01Z

0

You're trying to declare 2 different variables of the same name. Instead of declaring the second one, just use the one you already declared (take off inton the second usage).

...
    try
    {
        num = Convert.ToInt32(input); // <-- Using existing declaration here
        Console.WriteLine("This is element number " + num + " : " + randNums[num]);
    }
...

answered Feb 25, 2014 at 23:22

McAden

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Comments

Francis · Accepted Answer · 2014-02-25 23:26:25Z

0

You have two int variables with the same name. You need to change the other one since you have an int variable for the input that will accept the number assigned by the user, and another int variable responsible for detecting whether the number inputted is 999 or not.

answered Feb 25, 2014 at 23:26

Francis

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