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C # tutorial
When executing C# code, different errors can occur: coding errors made by the programmer, errors due to wrong input, or other unforeseeable things
When executing C# code, different errors can occur: coding errors made by the programmer, errors due to wrong input, or other unforeseeable things.
When an error occurs, C# will normally stop and generate an error message. The technical term for this is: C# will throw an exception (throw an error).
The try
statement allows you to define a block of code to be
tested for errors while it is being executed.
The catch
statement allows you to define a block of code to
be executed, if an error occurs in the try block.
The try
and catch
keywords
come in pairs:
try
{
// Block of code to try
}
catch (Exception e)
{
// Block of code to handle errors
}
Consider the following example, where we create an array of three integers:
This will generate an error, because myNumbers[10] does not exist.
int[] myNumbers = {1, 2, 3};
Console.WriteLine(myNumbers[10]); // error!
The error message will be something like this:
System.IndexOutOfRangeException: 'Index was outside the bounds of the
array.'
If an error occurs, we can use try...catch
to catch the error and execute some code to handle it.
In the following example, we use the variable inside the catch block (e
) together with the built-in Message
property, which outputs a message that describes the exception:
try
{
int[] myNumbers = {1, 2, 3};
Console.WriteLine(myNumbers[10]);
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
The output will be:
Index was outside the bounds of the array.
You can also output your own error message:
try
{
int[] myNumbers = {1, 2, 3};
Console.WriteLine(myNumbers[10]);
}
catch (Exception e)
{
Console.WriteLine("Something went wrong.");
}
The output will be:
Something went wrong.
The finally
statement lets you execute code, after try...catch
, regardless of the result:
try
{
int[] myNumbers = {1, 2, 3};
Console.WriteLine(myNumbers[10]);
}
catch (Exception e)
{
Console.WriteLine("Something went wrong.");
}
finally
{
Console.WriteLine("The 'try catch' is finished.");
}
The output will be:
Something went wrong.
The 'try catch' is finished.
The throw
statement allows you to create a custom error.
The throw
statement is used together with an exception class. There are many exception classes available in C#: ArithmeticException
,
FileNotFoundException
,
IndexOutOfRangeException
, TimeOutException
, etc:
static void checkAge(int age)
{
if (age < 18)
{
throw new ArithmeticException("Access denied - You must be at least 18 years old.");
}
else
{
Console.WriteLine("Access granted - You are old enough!");
}
}
static void Main(string[] args)
{
checkAge(15);
}
The error message displayed in the program will be:
System.ArithmeticException: 'Access denied - You must be at least 18 years old.'
If age
was 20, you would not get an exception:
checkAge(20);
The output will be:
Access granted - You are old enough!