Common C# Build-Time Errors: Part I

Here’s the situation:

You’ve written a program in C#. You’ve checked the flowcharts, examined your coding and developed your user interface.

You’re anticipating that everything will flow as smooth as silk. You’re ready to create a build of the program and, instead of seeing a beautiful, efficient result, you get several (often incomprehensible) error message. How did this happen?

Here are SOME ways that these errors occur:

#1 Undeclared Variables

C# throws an error message on undeclared variables. This most frequently happens in one of three ways:

1) The variable is not assigned a type.
The code in a “for-next loop” that reads like this:

for (nextStep = 0; nextStep < 20; nextStep++)
{
// loop process
}

should read like this:

for (int nextStep = 0; nextStep < 20; nextStep++)
{
// loop process
}

2) The variable name is spelled differently.
Variables are case sensitive in C#, which can lead to some careless errors:

for (int nextStep = 0; nextStep < 20; nextStep++)
{
int workerID = nextStep;
Console.WriteLine("Worker ID #:" +  WorkerId);
}

The compiler will view “workerID” and “WorkerId” as two different variables and view “WorkerId” as undeclared.

3) The variable is declared in a different scope.
In order to use variables both inside and outside a routine (such as a “for” loop or a “while “ loop), the variable must be declared outside the routine.

for (int nextStep = 0; nextStep < 20; nextStep++)
{
int workerID = nextStep;
}
Console.WriteLine("Worker ID #:" +  workerID);

This code will not display the final number in the sequence, but will throw an error due to the workerID variable’s declaration sitting inside the for loop.

#2 Variable Conversion Errors

For developers new to C#, especially those coming from more intuitive platforms such as VB.Net or ASP.Net, the lack of flexibility with variable types can be a hurdle.

Here’s an example of a variable conversion that throws a build-time error:

class MyClass
{
static public float TripleFloat(float t)
{
float fResult = 3.0 * t;
return fResult;
}
}

Since 3.0 is a “double”-type variable, the operation will return a “double”, not a “float”, and create a build-time error. The operation needs to recast the result as a “float” to avoid the conflict:

class MyClass
{
static public float TripleFloat(float t)
{
float fResult = (float)(3.0 * t);
return fResult;
}
}

#3 Protection Level Conflicts

Some programmers may forget that the default protection level for a class is “internal” and the default level for any member in that class is “private”.

class MyFirstClass  //default protection = internal
{
public void NameFunction(){
MySecondClass sc = new MySecondClass();
sc.strFirstName = "Harry";
sc.strLastName = "Potter";
Console.WriteLine("Name: " + sc.strFirstName + " " + sc.strLastName);
}
}

public class MySecondClass
{
string strFirstName = "Ron";
string strLastName = "Weasley"; //default protection = private
}

The “public” declaration for MySecondClass does not make its variables public automatically.  In order for MyFirstClass to access the variables from MySecondClass, both MyFirstClass and the two string variables in MySecondClass must also be set to “public”.

These are only a few of the routine errors that C# programmers encounter on a regular basis. In future articles, we will explore more of these errors, including those dealing with classes and inheritance, and how to correct them.