Statements and Blocks

Statements: A statement is a command given to the computer that instructs the computer to take a specific action, such as display to the screen, or collect input. A computer program is made up of a series of statements.

In C, a statement can be any of the following:

Labeled Statements: A statement can be preceded by a label. Three types of labels exist in C.

A simple identifier followed by a colon (:) is a label. Usually, this label is the target of a goto statement.

Within switch statements, case and default labeled statements exist. A statement of the form

case constant-expression : statement

indicates that control will pass to this statement if the value of the control expression of the switch statement matches the value of the constant-expression.

A statement of the form

default : statement

indicates that control will pass to this statement if the control expression of the switch statement does not match any of the constant-expressions within the switch statement. If the default statement is omitted, the control will pass to the statement following the switch statement. Within a switch statement, there can be only one default statement, unless the switch statement is within another switch statement.

Compound Statements: A compound statement is the way C groups multiple statements into a single statement. It consists of multiple statements and declarations within braces (i.e. { and }).
Expression statements: An expression statement consists of an optional expression followed by a semicolon (;). If the expression is present, the statement may have a value. If no expression is present, the statement is often called the null statement.

The printf function calls are expressions, so statements such as printf (“Hello World!\n”); are expression statements.

Selection Statement: Selection Statements in C programming are used to make decisions based on the conditions. It is also called as branching as a program decides which statement to execute based on the result of the evaluated condition. Three types of selection statements exist in C:

In this type of if-statement, the sub-statement will only be executed iff the expression is non-zero.

if ( expression ) statement

In this type of if-statement, the first sub-statement will only be executed iff the expression is non-zero; otherwise, the second sub-statement will be executed.

if ( expression ) statement else statement

Switch statements are also a type of selection statement. They have the format:
```
switch ( expression ) statement
```
The expression here is an integer or a character. The statement here is usually compound and it contains case-labeled statements and optionally a default-labeled statement.

Iteration Statement: An iteration statement, or loop, repeatedly executes a statement, known as the loop body, until the controlling expression is false. C has three kinds of iteration statements.

The first is a while-statement with the form:
```
while ( expression )     statement
```
The sub-statement of a while runs repeatedly as long as the control expression evaluates to non-zero at the beginning of each iteration. If the control expression evaluates to zero the first time through, the substatement may not run at all.
The second is a do-while statement of the form

do statement
while ( expression ) ;

This is similar to a while loop, except that the controlling expression is evaluated at the end of the loop instead of the beginning and consequently the sub-statement must execute at least once.

The third type of iteration statement is the for-statement.
```
for ( expressionopt ; expressionopt ; expressionopt ) statement
```
1. Jump Statements: C has four types of jump statements.
The first, the goto statement, is used sparingly and has the form

  goto identifier ;

This statement transfers control flow to the statement labeled with the given identifier. The statement must be within the same function as the goto.

The second, the break statement, with the form

  break ;

is used within iteration statements and switch statements to pass control flow to the statement following the while, do-while, for, or switch.

The third, the continue statement, with the form
```
continue ;
```
is used within the sub-statement of iteration statements to transfer control flow to the place just before the end of the substatement. In for statements the iteration expression will then be executed before the controlling expression is evaluated.
The fourth type of jump statement is the return statement with the form
```
return expressionopt ;
```
This statement returns from the function. If the function return type is void, the function may not return a value; otherwise, the expression represents the value to be returned.

Blocks: Blocks are a way of solving the scoping problem. A block is a program region containing definitions of variables and that delimits the regions where these definitions apply. In C programming language, a block is created using a pair of curly braces. The beginning of the block is denoted by an open curly brace ‘{‘ and the end is denoted by a closing curly brace ‘}’. The block collects statements together into a single compound statements. There are two types of block:

Statement blocks
```
 if ( i == j)
     {
       printf("martin \n");
     }
```
The statement block containing the printf is only executed if the i == j expression evaluates to TRUE.

Function blocks

 int add( int a, int b)      /* Function definition */
 {
   int c;
   c = a + b;
   return c;
 }

The statements in this block will only be executed if the add function is called.

PPS

Programming for Problem Solving

Statements and Blocks