Sometimes you have a value of one type but you need it as another type. Maybe you read a number from the console as a string, but you need to do math with it. Converting between types is called casting, and C# gives you several ways to do it.
Implicit Casting (Automatic)
C# automatically converts one type to another when there's no risk of losing data. This always goes from a smaller to a larger type — like fitting a small box inside a bigger box:
int myInt = 100;
double myDouble = myInt; // Implicit: int to double, works fine
Console.WriteLine(myDouble); // Prints 100
// float to double also works
float myFloat = 3.14f;
double anotherDouble = myFloat;
Implicit casting works for: int → long → float → double, and also int → double. Data can never be lost this way.
Explicit Casting (Manual)
When you might lose data — like converting a double to an int (which drops the decimal part) — you need explicit casting. You put the target type in parentheses before the value:
double myDouble = 9.78;
int myInt = (int)myDouble; // Explicit: double to int
Console.WriteLine(myInt); // Prints 9 (the .78 is truncated, not rounded)
Explicit casting is telling the compiler, "I know what I'm doing, go ahead." But be careful — you can lose data without getting any error.
The Convert Class
The Convert class provides more robust conversion methods. Unlike explicit casting, Convert rounds instead of truncating:
double myDouble = 9.78;
int myInt = Convert.ToInt32(myDouble); // Rounds to 10
Console.WriteLine(myInt); // Prints 10
string numberStr = "123";
int parsed = Convert.ToInt32(numberStr); // String to int
Console.WriteLine(parsed); // Prints 123
Convert.ToInt32 converts a value to an int. There are similar methods for other types: ToDouble, ToString, ToBoolean, etc.
Parse Methods
Every built-in type has a Parse method that converts a string to that type:
string ageStr = "25";
int age = int.Parse(ageStr);
string priceStr = "19.99";
double price = double.Parse(priceStr);
string flagStr = "true";
bool flag = bool.Parse(flagStr);
Console.WriteLine(age + 5); // Prints 30 (it's a real number now)
Parse throws an error if the string isn't valid. For safer conversion, you can use TryParse, which returns true/false instead of crashing.