Composite formatting in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is composite formatting in C#?

Composite formatting is a way to create formatted strings by embedding placeholders like {0}, {1}, etc., in a string, which are replaced by values provided as arguments.

beginner

How do you write a placeholder for the second argument in composite formatting?

You write it as {1} because placeholders start counting from zero, so {0} is the first argument, {1} is the second, and so on.

beginner

What will this code output? <br>

Console.WriteLine("Hello, {0}! Today is {1}.", "Alice", "Monday");

It will output: Hello, Alice! Today is Monday.

intermediate

How can you format a number to show two decimal places using composite formatting?

Use a format specifier inside the placeholder like {0:F2}, where F2 means fixed-point with 2 decimals. Example: <br>

Console.WriteLine("Price: {0:F2}", 3.14159);

outputs "Price: 3.14".

intermediate

What happens if you provide fewer arguments than placeholders in composite formatting?

You get a runtime error (FormatException) because the placeholders expect matching arguments to replace them.

In composite formatting, what does {0} represent?

A The first argument to replace in the string

B The second argument to replace in the string

C A literal zero character

D A format specifier

{0} is the placeholder for the first argument passed after the format string.

What will this code print? <br>

Console.WriteLine("{1} scored {0} points.", 10, "Bob");

A 10 scored Bob points.

B Bob scored 10 points.

C Bob scored {0} points.

D Runtime error

Placeholder {1} is replaced by "Bob" and {0} by 10, so it prints "Bob scored 10 points."

How do you format a date using composite formatting to show only the year?

A {0:yyyy}

B {0:year}

C {0:Y}

D {0:yy}

The format specifier yyyy shows the full year in four digits.

What error occurs if placeholders exceed the number of arguments?

A NullReferenceException

B FormatException

C IndexOutOfRangeException

D No error, placeholders are ignored

FormatException is thrown when placeholders do not have matching arguments.

Which method uses composite formatting in C#?

A Console.WriteLine(string, params object[])

B Console.ReadLine()

C string.Concat()

D Console.Clear()

Console.WriteLine can take a format string with placeholders and arguments to format the output.

Explain how composite formatting works in C# and give an example.

Think about how you replace parts of a string with values.

What are common mistakes when using composite formatting and how can you avoid them?

Consider what happens if you forget an argument or use wrong placeholder numbers.