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Lesson 6 of 60 14 minBeginner

Strings, input and output

Read input from the user, build text with interpolation, and use the most important string methods.

Almost every program works with text: names, messages, file paths, user input. In C# text is a string, a sequence of characters.

Reading input

Greeting.cs

1Console.Write("What is your name? ");2string? name = Console.ReadLine();   // waits until Enter is pressed3Console.WriteLine("Hello, " + name + "!");

Output

What is your name? Ravi
Hello, Ravi!

Building strings

Program.cs

1string first = "Ravi";2int age = 25;3 4string a = "Name: " + first + ", age " + age;   // concatenation5string b = $"Name: {first}, age {age}";          // interpolation (preferred)6string c = $"Next year: {age + 1}";              // any expression in { }7string d = $"Price: {1499.5:F2}";                // format: 2 decimals8 9Console.WriteLine(b);10Console.WriteLine(d);

Output

Name: Ravi, age 25
Price: 1499.50

Escape sequences and verbatim strings

Write	To get
`\n`	a new line
`\t`	a tab
`\"`	a double quote inside a string
`\\`	a backslash

Program.cs

1Console.WriteLine("Line 1\nLine 2");2Console.WriteLine("She said \"Hi\"");3string path = @"C:\Projects\Steel\model.ifc";   // @ = verbatim: \ is literal4Console.WriteLine(path);

Output

Line 1
Line 2
She said "Hi"
C:\Projects\Steel\model.ifc

Inside a string: indexes and methods

Member	What it does
`s.Length`	number of characters
`s[i]`	the character at index `i` (a `char`)
`s.ToUpper()` / `s.ToLower()`	change case
`s.Trim()`	remove spaces at both ends
`s.Contains(x)`	`true` if `x` appears in `s`
`s.IndexOf(x)`	position of `x`, or `-1`
`s.Substring(start, length)`	part of the string
`s.Replace(a, b)`	replace every `a` with `b`
`s.Split(sep)`	cut into a `string[]`
`string.IsNullOrWhiteSpace(s)`	true for null, empty or only spaces

Comparing strings

Program.cs

1string a = "Steel";2string b = "steel";3 4Console.WriteLine(a == b);                                              // False5Console.WriteLine(a.Equals(b, StringComparison.OrdinalIgnoreCase));     // True

Output

False
True

Quick check

What does "Hello".Substring(1, 3) return?

Quick check

After string s = "hi"; s.ToUpper(); what is s?

Practice

Ask the user for their full name (e.g. “ ravi selva ”). Print it trimmed and in capitals, then print how many characters it has (without the outer spaces), and the first letter.

Show the solution

Solution.cs

1Console.Write("Full name: ");2string name = (Console.ReadLine() ?? "").Trim();3 4Console.WriteLine(name.ToUpper());5Console.WriteLine($"Length: {name.Length}");6if (name.Length > 0)7    Console.WriteLine($"First letter: {name[0]}");

Output

Full name:   ravi selva
RAVI SELVA
Length: 10
First letter: r

Remember

Console.ReadLine() returns a string; convert it for numbers.
Prefer interpolation: $"Hello {name}", with formats like {x:F2}.
Indexes start at 0; the last index is Length - 1.
Strings are immutable: store the result of ToUpper, Trim, Replace…

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