The rule specify how the character sequence will be grouped together, to form tokens. A smallest individual unit in C program is known as C Token. Tokens are either keywords, identifiers, constants, variables or any symbol which has some meaning in C language. A C program can also be called as a collection of various tokens.

For example, the following C statement consists of five tokens −

printf("Hello, World! \n");

The individual tokens are −

printf
(
   "Hello, World! \n"
)
;

Semicolons ;

In a C program, the semicolon is a statement terminator. Each statement which does not has its body (please note that, statement without its body) must be terminated by the semicolon (;). It indicates the end of one logical entity.

Given below are two different statements −

printf("Hello, World! \n");
return 0;

The statements which should be terminated

• All printf(), scanf() or any other function calls
• All declarations like variables, constants, function, structures must be terminated by semicolon.
• All expressions must be terminated by the semicolon (;).

The statements which should not be terminated

• Header files include statements.
• Macro definition statements.
• If statement, loop statements, function header with the function definitions

Comments

Comments are plain simple text in a C program that are not compiled by the compiler. We write comments for better understanding of the program. Though writing comments is not compulsory, but it is recommended to make your program more descriptive. It make the code more readable.

There are two ways in which we can write comments.

1. Using // This is used to write a single line comment
2. Using /* */: The statements enclosed within /* and */ , are used to write multi-line comments.

Example of comments :

// This is a comment

/* This is a comment */

/* This is a long 
and valid comment */

// this is not
  a valid comment

Some basic syntax rule for C program

1. C is a case sensitive language so all C instructions must be written in lower case letter.
   
2. All C statement must end with a semicolon.
3. Whitespace is used in C to describe blanks and tabs.
4. Whitespace is required between keywords and identifiers
5. Braces must always match upon pairs, i.e., every opening brace { must have a matching closing brace }
6. All C program starts with void main( ) function