Guide to breaking down and understanding C# errors

Intro

In this blog, I’m going to mainly focus on deciphering C# errors and potential steps to solve them. As I mentioned in my last blog, C# is statically typed, which allows the compiler to perform more optimization work ahead of time. One of the important features of C# is how it’s compiled.

Compile Time is…

Compile time refers to the period when the source code is being translated into machine code or an intermediate language by a compiler before the program actually runs (or even gets executed). In C#, this process happens when you build (or compile) your application (like all the code). The compiler checks your code for syntax errors, type mismatches, and other issues that would prevent the program from running correctly.

Compile time versus runtime…

I also mentioned in my last blog that JavaScript does runtime checks. I want to highlight the biggest difference between these two: C# detects errors at compile time, before the program runs, while JavaScript detects errors at runtime, when the program is already running. In JavaScript, the code continues to execute until it reaches an error.

Example compile-time errors:

randomData = "abc abc";
Console.WriteLine(randomData); 
// Error: all variables must be declared before they are assigned a value. 

int a = 10; 
string b = "Hello"; 

a = b;
 // Error: types are strictly enforced, meaning you cannot assign a string directly to an int without explicitly converting it.

string result = a + b;  
// Concatenation of an integer with a string requires explicit conversion before the concatenation can happen.

The program won't compile due to the errors. The compiler will produce error messages indicating the type mismatch, likely along the lines of:

/home/ccuser/workspace/csharp-data-types-variables-handling-errors-csharp_v2/Program.cs(9,7): error CS0103: The name 'randomData' does not exist in the current context [/home/ccuser/workspace/csharp-data-types-variables-handling-errors-csharp_v2/e7-workspace.csproj] 

We can break it down into 3 parts to read.
First, we have the full local path of the file where the error occurred, Program.cs. The numbers that follow in parentheses denote the line and character of the file responsible for the error, respectively. So, (9,7) indicates that the error is on line 9, starting at the 7th character (including spaces).

/home/ccuser/workspace/csharp-data-types-variables-handling-errors-csharp_v2/Program.cs(9,7): 
// Path to exact location separated from the next part by :

Next is the actual error, which will inform us what in our code is incorrect. Every kind of error in C# has a unique identifier, like “CS0103”, so that they can easily be found within the Microsoft documentation. This error indicates that a variable name was used without ever being defined:

error CS0103: The name 'randomData' does not exist in the current context 

Finally, a C# program requires a special type of file using the .csproj extension. The .csproj file itself does not generate error messages directly, but it dictates the build and deployment of metadata for the project. Checking the .csproj file is a good step to diagnose and resolve any issues related to missing dependencies, incorrect settings, or build misconfiguration.

[/home/ccuser/workspace/csharp-data-types-variables-handling-errors-csharp_v2/e7-workspace.csproj] 

Based on that, you can infer what the other two error messages look like:

• Error CS0103: The randomData variable is not declared before use.
• Error CS0029: You cannot assign a string (b) to an int (a) without explicit conversion.
• Error CS0019: You cannot use the + operator to concatenate an int with a string without converting the int to a string first.

These messages will explain why the code can't compile and point to the specific lines where the errors occur. You will need to fix these issues to make the code work, but now you know what issues your code is facing.

Sometimes, we don’t even need to find a solution—the error message will tell us exactly what the problem is.

int score = 45 // error CS1002: ; expected 

/home/ccuser/workspace/csharp-data-types-variables-handling-errors-csharp_v2/Program.cs(9,21): error CS1002: ; expected [/home/ccuser/workspace/csharp-data-types-variables-handling-errors-csharp_v2/e7-workspace.csproj]

The procedure to resolve a C# error...

1. Receive the error and break it down
   • First, identify the location of the error. Look for the file name, line number, and character position in the error message.
2. Read through the error message carefully
   • Understand what the error is telling you. This will often include information about what’s wrong (e.g., undeclared variables, type mismatches, etc.).
3. Search for the error code in Microsoft documentation
   • Go to the Microsoft documentation website, and use the error code (e.g., "CS0103") in the filter by title search bar to find the related documentation for that specific error.
4. Review the documentation and examples
   • Carefully read the explanation and solution examples provided in the documentation to understand how to resolve the issue.
5. Apply the solution in your code
   • Try the suggested solution or fix it in your own code. Make sure to test it and check if the error is resolved.

I hope this was helpful! Here’s a quick tip: Like JavaScript, C# variable names can contain letters, digits, and underscores, but not the dollar sign ($). While the compiler doesn’t enforce it, it’s also good practice to use camelCase, which is the standard convention in JavaScript.

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