Variables, types and strings

In a game, the player has a name, a score, lives left and a level. The program has to keep this information somewhere and change it as the game goes on. That is what variables are for. In C#, every variable has a type that decides what kind of value it can hold.

Variables

To declare a variable, write its type first, then its name, and assign a value with the = sign. Later you can give the variable a new value, but only of the same type. Names usually start with a lowercase letter, and each following word starts with a capital: playerName, livesLeft.

string playerName = "Leyla";
int score = 0;
int livesLeft = 3;
bool isGameOver = false;

score = score + 50;
score += 25;
livesLeft--;

Console.WriteLine(playerName);
Console.WriteLine(score);
Console.WriteLine(livesLeft);
Console.WriteLine(isGameOver);

Leyla
75
2
False

• score += 25 is short for score = score + 25; there are also -=, *= and /=.
• livesLeft-- decreases the value by 1, and ++ increases it by 1.
• A bool value is printed with a capital letter, True or False, but written in lowercase in code: true, false.

Basic types

`var` and `const`

When the type is obvious from the right-hand side, you can write var instead — the compiler works out the type itself. This does not mean the variable has no type: after var city = "Baku";, city stays a string forever. For values that must never change, use const.

var city = "Baku";
var year = 2026;
var price = 2.5m;
const int DaysInWeek = 7;

Console.WriteLine(city.GetType().Name);
Console.WriteLine(year.GetType().Name);
Console.WriteLine(price.GetType().Name);
Console.WriteLine(DaysInWeek * 4);

String
Int32
Decimal
28

GetType().Name shows the type's name in .NET: int is really a short name for Int32, and string for String. If you try city = 5;, the compiler reports error CS0029: an int cannot be converted to a string. And DaysInWeek = 8; is not allowed at all, because it is a constant.

Numbers and conversions

You already know that 7 / 2 gives 3. If you need a fractional result, convert one of the numbers to double: (double)7 / 2. This is called a cast. In the other direction, (int)3.99 drops the fractional part and gives 3 — it does not round! To turn text into a number, use int.Parse; to turn a number into text, use ToString().

using System.Globalization;

CultureInfo.CurrentCulture = CultureInfo.InvariantCulture;

int apples = 7;
int friends = 2;
Console.WriteLine(apples / friends);
Console.WriteLine((double)apples / friends);
Console.WriteLine((int)3.99);
Console.WriteLine(Math.Round(3.99));

int year = int.Parse("2026");
Console.WriteLine(year + 1);
Console.WriteLine(year.ToString() + "!");

3
3.5
3
4
2027
2026!

Strings and interpolation

Building text with + quickly gets tiring. String interpolation is easier: put $ before the string and write variables and expressions straight into the text inside curly braces. After a colon inside the braces you can add a format: F2 means two digits after the decimal separator, N0 a whole number with thousands separators.

using System.Globalization;

CultureInfo.CurrentCulture = CultureInfo.InvariantCulture;

string name = "Murad";
int score = 95;
decimal price = 4.5m;
int views = 1234567;

Console.WriteLine("Hi, " + name + "!");
Console.WriteLine($"{name} scored {score} points.");
Console.WriteLine($"Next time: {score + 5}");
Console.WriteLine($"3 tickets: {price * 3:F2} AZN");
Console.WriteLine($"Views: {views:N0}");

Hi, Murad!
Murad scored 95 points.
Next time: 100
3 tickets: 13.50 AZN
Views: 1,234,567

A string is an object too, with useful properties and methods. Note that strings are immutable: methods like ToUpper() do not change the original but return a new string. Characters are accessed by index, and counting starts at zero.

string city = "  Baku  ";
string clean = city.Trim();

Console.WriteLine(clean.Length);
Console.WriteLine(clean.ToUpper());
Console.WriteLine(clean.Contains("ak"));
Console.WriteLine(clean.Replace("Baku", "Ganja"));
Console.WriteLine(clean[0]);
Console.WriteLine($"[{city}]");

4
BAKU
True
Ganja
B
[  Baku  ]