Data Types

Every piece of data in C# has a type. Types tell the compiler what kind of data you're working with — numbers, text, true/false values, and more. Picking the right type is like picking the right tool for a job.

Common Data Types

Here are the types you'll use most often:

int count = 100;              // Whole numbers (-2 billion to 2 billion)
long population = 8000000000; // Big whole numbers
float price = 19.99f;         // Single-precision decimal (f suffix)
double pi = 3.1415926535;     // Double-precision decimal (default for decimals)
decimal money = 49.99m;       // High-precision for financial (m suffix)
bool isReady = true;          // true or false
char grade = 'A';             // Single character (single quotes)
string message = "Hello";     // Text (double quotes)
    

Notice the suffixes: f for float, m for decimal. These tell the compiler "yes, I really want this specific type." Without them, C# defaults decimal numbers to double.

Which Type Should You Use?

• int — your go-to for whole numbers. 99% of the time, this is what you need.
• double — your go-to for decimal numbers. It's precise enough for most calculations.
• decimal — use for money, currencies, and anything where precision matters. It avoids rounding errors that double sometimes has.
• bool — for yes/no, true/false, on/off conditions.
• string — for text. You'll use this constantly.
• char — for a single character. Less common, but useful when you need exactly one letter.

Value Types vs Reference Types

This is a big concept in C#. Types fall into two categories:

Value types store their data directly. When you assign one value type to another, a copy is made. int, double, bool, char, float, decimal — these are all value types.

int a = 10;
int b = a;   // b gets a copy of a's value
a = 20;      // a changes, but b is still 10
Console.WriteLine(b);  // Prints 10
    

Reference types store a reference (think of it as an address) to where the data lives. When you assign one reference type to another, both point to the same data. string is a reference type (though it behaves like a value type in many ways).

string first = "Hello";
string second = first;  // Both point to the same string
    

We'll dive deeper into this later, but for now, just know the difference exists.