One use of typecasts is to force the correct type of mathematical operation to take place. It turns out that in C and C (and other programming languages), the result of the division of integers is itself treated as an integer: for instance, 3/5 becomes 0! Well, 3/5 is less than 1, and integer division ignores the remainder. The size of different types can be discovered with the sizeof operator. It returns the size of the variable ( or structure) in bytes (8 bits). The following program will print out the sizes of the different types. Sep 18, 2010 C Programming Tutorial - 3 - Introduction to Variables thenewboston. C 5 - Variables and Data types. VoidRealms 16,883 views. 22 videos Play all Dev C. One use of typecasts is to force the correct type of mathematical operation to take place. It turns out that in C and C (and other programming languages), the result of the division of integers is itself treated as an integer: for instance, 3/5 becomes 0!
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Variables, types, and operators Lecture3 CS 113 – Fall 2007 2 AnnouncementsAnnouncements Assignment 1 online, due next Wednesday Check newsgroup for clarifications, corrections, etc. Need a partner? Check newsgroup. C compiler options Dev-C is now installed in CIT lab in Phillips 318 Xcode on Macs in CIT labs. Variables and types The usefulness of the 'Hello World' programs shown in the previous chapter is rather questionable. We had to write several lines of code, compile them, and then execute the resulting program, just to obtain the result of a simple sentence written on the screen.
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A variable provides us with named storage that our programs can manipulate. Each variable in C++ has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.
The name of a variable can be composed of letters, digits, and the underscore character. It must begin with either a letter or an underscore. Upper and lowercase letters are distinct because C++ is case-sensitive −
There are following basic types of variable in C++ as explained in last chapter −
Sr.No | Type & Description |
---|---|
1 | bool Stores either value true or false. |
2 | char Typically a single octet (one byte). This is an integer type. |
3 | int The most natural size of integer for the machine. |
4 | float A single-precision floating point value. |
5 | double A double-precision floating point value. |
6 | void Represents the absence of type. |
7 | wchar_t A wide character type. |
C++ also allows to define various other types of variables, which we will cover in subsequent chapters like Enumeration, Pointer, Array, Reference, Data structures, and Classes.
Following section will cover how to define, declare and use various types of variables.
Variable Definition in C++
Dev C Variable Types Examples
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A variable definition tells the compiler where and how much storage to create for the variable. A variable definition specifies a data type, and contains a list of one or more variables of that type as follows −
Here, type must be a valid C++ data type including char, w_char, int, float, double, bool or any user-defined object, etc., and variable_list may consist of one or more identifier names separated by commas. Some valid declarations are shown here −
The line int i, j, k; both declares and defines the variables i, j and k; which instructs the compiler to create variables named i, j and k of type int.
Variables can be initialized (assigned an initial value) in their declaration. The initializer consists of an equal sign followed by a constant expression as follows −
Some examples are −
For definition without an initializer: variables with static storage duration are implicitly initialized with NULL (all bytes have the value 0); the initial value of all other variables is undefined.
Variable Declaration in C++
A variable declaration provides assurance to the compiler that there is one variable existing with the given type and name so that compiler proceed for further compilation without needing complete detail about the variable. A variable declaration has its meaning at the time of compilation only, compiler needs actual variable definition at the time of linking of the program.
A variable declaration is useful when you are using multiple files and you define your variable in one of the files which will be available at the time of linking of the program. You will use extern keyword to declare a variable at any place. Though you can declare a variable multiple times in your C++ program, but it can be defined only once in a file, a function or a block of code.
Example
Try the following example where a variable has been declared at the top, but it has been defined inside the main function −
When the above code is compiled and executed, it produces the following result −
Same concept applies on function declaration where you provide a function name at the time of its declaration and its actual definition can be given anywhere else. For example −
Lvalues and Rvalues
There are two kinds of expressions in C++ −
- lvalue − Expressions that refer to a memory location is called 'lvalue' expression. An lvalue may appear as either the left-hand or right-hand side of an assignment.
- rvalue − The term rvalue refers to a data value that is stored at some address in memory. An rvalue is an expression that cannot have a value assigned to it which means an rvalue may appear on the right- but not left-hand side of an assignment.
Variables are lvalues and so may appear on the left-hand side of an assignment. Numeric literals are rvalues and so may not be assigned and can not appear on the left-hand side. Following is a valid statement −
But the following is not a valid statement and would generate compile-time error −
Dev C++ Variable Types Chart
In C++, variables must be declared and they must be assigned a type. Fortunately, C++ provides a number of variable types. See the table for a list of variables, their advantages, and limitations.
Variable | Defining a Constant | What It Is |
---|---|---|
int | 1 | A simple counting number, either positive or negative. |
short int | -- | A potentially smaller version of int. It uses less memory but has a smaller range. |
long int | 10L | A potentially larger version of int. There is no difference between long and int with gcc |
long long int | 10LL | A potentially even larger version of int. |
float | 1.0F | A single precision real number. This smaller version takes less memory than a double but has less accuracy and a smaller range. |
double | 1.0 | A standard floating-point variable. |
long double | -- | A potentially larger floating-point number. On the PC, long double is used for the native size of the 80×86 floating-point processor, which is 80 bits. |
char | ‘c’ | A single char variable stores a single alphabetic or digital character. Not suitable for arithmetic. |
wchar_t | L’c’ | A larger character capable of storing symbols with larger character sets like Chinese. |
char string | “this is a string” | A string of characters forms a sentence or phrase. |
bool | true | The only other value is false. |
The long long int and long double were officially introduced with C++ ‘11.
The integer types come in both signed and unsigned versions. Signed is always the default (for everything except char and wchar_t). The unsigned version is created by adding the keyword unsigned in front of the type in the declaration. The unsigned constants include a U or u in their type designation. Thus, the following declares an unsigned int variable and assigns it the value 10:
The following statement declares the two variables lVariable1 and lVariable2 as type long int and sets them equal to the value 1, while dVariable is a double set to the value 1.0. Notice in the declaration of lVariable2 that the int is assumed and can be left off:
You can declare a variable and initialize it in the same statement:
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A char variable can hold a single character; a character string (which isn’t really a variable type but works like one for most purposes) holds a string of characters. Thus, ‘C’ is a char that contains the character C, whereas “C” is a string with one character in it.
C# Date Variable Types
A rough analogy is that a ‘C’ corresponds to a nail in your hand, whereas “C” corresponds to a nail gun with one nail left in the magazine.
C Data Types
If an application requires a string, you’ve gotta provide one, even if the string contains only a single character. Providing nothing but the character just won’t do the job.