CODEWITHSUNDEEP
c#
Abijeet Patro
Abijeet Patro

Reputation: 2884

Reason for use of unassigned local variable error

I'm just wondering why the compiler gives me this error. The try block will be executed every time the function is called and that means the variable will get assigned. But still it doesn't let me compile.

using System;

namespace Checking
{
    class Program
    {
        static void Main(string[] args)
        {
            int intNum;
            intNum = readValue("Please enter a number: ");

        }
        static int readValue(string strPrompt)
        {
            int intRes;
            Console.WriteLine(strPrompt);
            try
            {
                intRes = Convert.ToInt32(Console.ReadLine());   // Gets assigned here! But still doesnt allow me to compile!

            }
            catch (Exception ex)
            {
                Console.WriteLine("Please enter a numeric value.\n");
                readValue(strPrompt);
            }
            return intRes;    
        }
    }
}

Putting return intRes inside the try block allows me to get rid of that error, but then an error crops up saying not all code paths return a value. I understand the errors, but I still don't understand why it won't allow me to compile, the try block gets executed every time right?

I also know that assigning 0 to intRes will get rid of that error.

Regards,

Upvotes: 0

Views: 1516

Answers (5)

Guffa
Guffa

Reputation: 700152

The compiler is right. The variable is not always assigned.

If the conversion fails, the assignment never happens, and the execution continues inside the catch block, where you call the function again, but you have forgotten to assign the return value of that call to the variable:

catch (Exception ex)
{
  Console.WriteLine("Please enter a numeric value.\n");
  intRes = readValue(strPrompt);
}

Here's an anternative implementation using a while and TryParse:

static int readValue(string strPrompt) {
  int intRes = 0;
  bool done = false;
  while (!done) {
    Console.WriteLine(strPrompt);
    if (Int32.TryParse(Console.ReadLine(), out intRes) {
      done = true;
    } else {
      Console.WriteLine("Please enter a numeric value.\n");
    }
  }
  return intRes;    
}

Upvotes: 3

Steve
Steve

Reputation: 216243

The compiler has no way to know if your code inside the try block will throw an exception or not.
So, in case your code throws an exception, then the intRes variable will never be assigned.

Consequently the compiler emits the error message.

Also, as it stands, your code has a problem. You try to recursively call readValue inside the catch block to get a correct value but when your user finally enter a correct value, the main will never receive the value entered because you are using a local variable for the result value.

Upvotes: 1

podiluska
podiluska

Reputation: 51494

Because if the try fails, intRes has no value

In your catch use

intRes = readValue(strPrompt);

Initialise it with 

int intRes = 0;

instead of

int intRes;

You may also want to look at the int.TryParse syntax

Upvotes: 3

cyon
cyon

Reputation: 9538

You will get an uninitialized intRes if Console.ReadLine() throws an exception. That is why your compiler is complaining.

Upvotes: 2

Oded
Oded

Reputation: 498904

If Convert.ToInt32 failes, intRes never gets assigned to.

Either set a default value when creating the variable, or assign to in the catch block.

Upvotes: 3

Related Questions