Data types, numbers and type conversion — C# Language

3. Data types, numbers and type conversion

Basic★ Must knowLesson 3 of 38

C# keyword	.NET type	Size	Range / precision	Literal
`byte` / `sbyte`	`Byte` / `SByte`	1 byte	0–255 / −128–127	`255`
`short` / `ushort`	`Int16` / `UInt16`	2 bytes	±32,767 / 0–65,535	`100`
`int` / `uint`	`Int32` / `UInt32`	4 bytes	±2.1 billion	`42`, `42u`
`long` / `ulong`	`Int64` / `UInt64`	8 bytes	±9.2 × 10¹⁸	`42L`
`float`	`Single`	4 bytes	~6–9 digits, binary floating point	`1.5f`
`double`	`Double`	8 bytes	~15–17 digits, binary floating point (default for decimals)	`1.5`
`decimal`	`Decimal`	16 bytes	28–29 digits, base-10 — use for money	`1.5m`
`char`	`Char`	2 bytes	One UTF-16 code unit	`'A'`
`bool`	`Boolean`	1 byte	`true` / `false`	`true`
`string`	`String`	reference	Immutable text	`"text"`
`object`	`Object`	reference	Base of every type	—

csharp

Console.WriteLine(0.1 + 0.2 == 0.3);       // False — binary floating point can't store 0.1 exactly
Console.WriteLine(0.1m + 0.2m == 0.3m);    // True  — decimal is exact for base-10 values
int big = 1_000_000;                        // digit separators
int hex = 0xFF, bin = 0b1010;

// Integer overflow wraps silently by default...
int max = int.MaxValue;
int wrapped = unchecked(max + 1);           // -2147483648
// ...unless you ask for checking
try { int boom = checked(max + 1); } catch (OverflowException) { Console.WriteLine("Overflow!"); }

Console.WriteLine(7 / 2);     // 3   — integer division truncates
Console.WriteLine(7 / 2.0);   // 3.5
Console.WriteLine(7 % 2);     // 1   — remainder
Console.WriteLine(Math.Round(2.5));                              // 2 — banker's rounding (to even) by default
Console.WriteLine(Math.Round(2.5, MidpointRounding.AwayFromZero)); // 3

Type conversion:

Kind	Example	Notes
Implicit (widening)	`long l = intValue; double d = intValue;`	Safe, no data loss, no syntax needed
Explicit cast (narrowing)	`int i = (int)3.99;` → `3`	May lose data; truncates decimals
`Convert` class	`Convert.ToInt32("42")`, `Convert.ToInt32(3.5)` → `4`	Rounds to even; `null` → 0
`Parse`	`int.Parse("42")`	Throws `FormatException` on bad input
`TryParse`	`int.TryParse(input, out var n)`	Returns `false` instead of throwing — use for user input
`as` / `is`	`obj as string`, `obj is int n`	Reference/pattern conversions without exceptions

csharp

if (int.TryParse(Console.ReadLine(), out int qty) && qty > 0)
    Console.WriteLine($"Ordering {qty}");
else
    Console.WriteLine("Please enter a positive number");

decimal price = decimal.Parse("1,234.50", NumberStyles.Number, CultureInfo.InvariantCulture); // culture decides what , and . mean

Interview tip: "Why decimal for money?" — double is binary and can't represent 0.1 exactly, so sums drift (0.1 + 0.2 != 0.3). decimal stores base-10 digits exactly, at the cost of speed and memory.