Basics in

About Basics

C is a statically typed language, which means that everything has a type at compile-time. Choosing a name for a variable and setting its type is referred to as declaring a variable.

A variable is declared by explicitly specifying its type. A variable name must follow some rules like starting with either a letter or an underscore. Some names cannot be used as they are reserved for keywords or other identifiers.

Setting or updating the variable is done by variable assignment. Setting the value defines that variable. Defining the variable is also known as initialization.

int foo;      // Declare an integer named var
foo = 10;     // Define the variable

int bar = 15; // Both can also be done in a single statement

The value of a variable can be assigned and updated using the = simple assignment operator. Once defined, a variable's type can never change.

int foo = 10; // Assign initial value
foo = 25;     // Update to new value

foo = false;  // Compiler error when assigning value of a different type

C is an imperative procedural language. All computation is carried out as part a series of statements that are part of a [function][] or multiple functions.

Each function can have zero or more parameters. When defining a function all parameters, and the return value must be explicitly typed. Values are returned from functions using the return keyword. Functions have external storage class by default, meaning that it exists for the lifetime of the program and can be visible externally to the file. To prevent this the static keyword can be added to specify internal visibility.

static int add(int x, int y) {
  return x + y;
}

In the above example, the variables x and y can only be used within the function that is, they have function scope. Scope is the idea that the value associated with a name (of a program element) is only accessible within the code "area" where it is defined. The principal code areas in C are:

• file
• function
• block (such as within loops and other constructs)

Functions are invoked by specifying the function name and passing arguments for each of the function parameters.

int sum = add(1, 2);

C supports two types of comments. Single line comments are preceded by // (since C99) and multi-line comments are inserted between /* and */.