What is null statement ?

Answer: 

A "null statement" is a statement containing only a semicolon; it can appear wherever a statement is expected. Nothing happens when a null statement is executed. The correct way to code a null statement is:

General form:

               ;

Example:

Statements such as do, for, if, and while require that an executable statement appear as the statement body. The null statement satisfies the syntax requirement in cases that do not need a substantive statement body.

As with any other C statement, you can include a label before a null statement. To label an item that is not a statement, such as the closing brace of a compound statement, you can label a null statement and insert it immediately before the item to get the same effect.

This example illustrates the null statement:

for ( i = 0; i < 10; line[i++] = 0 )

     ;

In this example, the loop expression of the for statement line[i++] = 0 initializes the first 10 elements of line to 0. The statement body is a null statement, since no further statements are necessary.