4.1. Values and Data Types¶
Programs may be thought of as being made up of two things:
Operations that manipulate data
This chapter focuses primarily on the first of these two fundamental components, data.
Data can be stored in a program in a variety of ways. The most basic unit of data is a value.
A value is a specific piece of data, such as a word or a number.
Some examples are
Each value belongs to a category called a data type. We will see many
different data types throughout the course, the first three of which are the
int, double, and string types. Whole numeric values such as
ints. Doubles deal with decimal points, some examples include
3.14159265. Sequences of characters enclosed in double quotes, such as
"Hello, World!", are strings, so-called because they contain a string of
letters. Strings must be enclosed in double quotes.
If you are not sure what data type a value falls into, follow the value with
1 2 3
Console.WriteLine(("Hello, World!").GetType()); Console.WriteLine(17.GetType()); Console.WriteLine(3.14.GetType());
System.String System.Int32 System.Double
Not surprisingly, C# reports that the data type of
"Hello, World!" is
The data type of
17 is assumed
int because it is a whole number, and
double because of the decimal point.
Console.WriteLine(("Hello, World!").GetType()); prints out
System.String to the console. The
GetType method is not printed to the console because the statement
"Hello, World!" GetType is an expression. Briefly, expressions are code segments that are reduced to a value. We will learn more about expressions soon.
GetType is a C# entity known as an method. It carries out some kind of action, which is already built into it.
There are data types other than string and number, including object and method, which we will learn about in future chapters.
4.1.1. More On Strings¶
What about values like
"3.2"? They look like numbers, but they are in double
quotation marks making them strings.
Double-quoted strings can contain single quotes inside them, as in
4.1.2. More On Numbers¶
When you type a large integer value, you might be tempted to use commas between groups of
three digits, as in
42,000. This is not a legal integer in C#.
42000 error CS1502: ...`System.Console.WriteLine(string, object)' has some invalid arguments
Well, that’s not what we expected at all!
Because of the comma, C# chose to treat
42,000 as a pair separate entries.
This causes an error in the Console.WriteLine() which was built to only work with a single entry.
Adding additional entries separated by commas will overload it, causing an error.
Remember not to put commas or spaces in your integers, no matter how big they are. Also revisit what we said in the chapter How Programs Work: formal languages are strict, the notation is concise, and even the smallest change might mean something quite different from what you intend.
4.1.3. Type Systems¶
Every programming language has a type system, which is the set of rules that determine how the languages deals with data of different types. In particular, how values are divided up into different data types is one characteristic of a type system.
When discussing the differences between programming languages, the details of type systems are one of the main factors that programmers consider. There are other aspects of type systems beyond just how values are categorized. We will explore these in future lessons.
4.1.4. Check Your Understanding¶
Which of these is not a data type in C#?