Introduction to Variables in C Programming: Types, Definition, and Lvalues & Rvalues, Lecture notes of C programming

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University of Central Florida

COP 3223C

Introduction to Programming in C

• (^) A variable is nothing but a name given to a

storage area 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
  • (^) The set of operations that can be applied to the variable

• (^) char
  • (^) Typically a single octet (one byte).
  • (^) This is an integer type
• (^) int
  • (^) The most natural size of integer for the machine
• (^) float
  • (^) A single-precision floating point value
• (^) double
  • (^) A double-precision floating point value
• (^) void
  • (^) Represents the absence of type

• (^) C programming language also allows to define

various other types of variables, which we will

cover in subsequent lectures about

• (^) Enumeration
• (^) Pointer
• (^) Array
• (^) Structure
• (^) Union
• (^) For this lecture, we will study only basic

variable types

• (^) Variable Definition in C
  • (^) type must be a valid C data type including char, w_char, int, float, double, bool, or any user-defined object
  • (^) variable_list may consist of one or more identifier names separated by commas

• (^) Variable Definition in C
  • (^) Some valid declarations are shown here
  • (^) The line int i, j, k; declares and defines the variables i, j, and k; which instruct the compiler to create variables named i, j and k of type int.

• (^) Variable Definition in C
  • (^) 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 are undefined

• (^) Variable Definition in C
  • (^) A variable declaration provides assurance to the compiler that there exists a variable with the given type and name so that the compiler can proceed for further compilation without requiring the complete detail about the variable.
  • (^) A variable definition has its meaning at the time of compilation only, the compiler needs actual variable definition at the time of linking the program.

• (^) Example
  • (^) The example, where variables have been declared at the top, but they have been defined and initialized inside the main function

• (^) Variable Definition in C
  • (^) The 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.
  • (^) Example

• (^) Lvalues and Rvalues in C
  • (^) There are two kinds of expressions in C −
    • (^) lvalue
      • (^) Expressions that refer to a memory location are called "lvalue" expressions.
      • (^) 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-hand side but not on the left-hand side of an assignment.

• (^) Lvalues and Rvalues in C
  • (^) Variables are lvalues and so they may appear on the left-hand side of an assignment.
  • (^) Numeric literals are rvalues and so they may not be assigned and cannot appear on the left-hand side.
  • (^) Take a look at the following valid and invalid statements