Decision control statements

Conditional Statesments

if statement

• It is a statement used to execute a piece of code based on a given condition.
• The statement is executed if the Boolean-expression evaluates to true.

          Syntax:
                   if (expression)
                    statement;

• If the Boolean-expression evaluates to false then the statement will be skipped and another statement (if exists) will be executed.

Example:

Output:

if-else statement

• If all the if block statements are false, then else block statement is executed, i.e., statements present inside the else block is executed, if the Boolean-expression of the if statement is not satisfied.

          Syntax:
                  if (expression)
                  statement;
                  else
                  statement;

                  Remember, only one statement can appear directly, i.e., either if or the else. 

Example:

Output:

if else if statement / if-else-if ladder

• if-else-if ladder is a programming construct that is based on a sequence of nested ifs.

          Syntax:
                  if(expression)
                  {
                                   statement;
                  }
                    else if(expression)
                  {
                                   statement;
                  }
                   else if(expression)
                  {
                                   statement;
                  }
                   else
                  {
                                   statement;
                   }

• The if statements are executed from the top-down. If one of the conditions of the if statement is satisfied, then the statement associated with that particular if is executed, the rest of the ladder is bypassed.
• Among all the conditions, if none of the conditions is true, then the else statement will be executed at the end.
• The final else statement acts as a default condition.
• If the final else statement is not present at the end and all other conditions are not satisfied, then no action will be taken.

Example:

Output:

Nested if statements

• A nested if statement uses if statements inside if statements. i.e., if statements present inside another if statement is known as Nested if. 
• It is used when we have multiple if conditions.
• In Nested if, one if statement targets another if statement. 

          Syntax:
                    if(expression)
                    {
                              statement;
                              if(expression)
                              {
                                        statement;
                              }
                    }

Example:

Output:

for loop

• Loops (also called iteration statements) allow a collection of instructions to execute repeatedly until a certain condition is reached.

                  Syntax:
                         for (initialization; condition; increment)
                          {
                                  statement
                          }

There are many variations of for loop, but its most common form works like this:

• The initialization is used to set the loop control variable, and it assigns an initial value to it.
• The condition of the for loop is a relational expression that defines the exit of the loop.
• The increment defines the variation in the loop control variable at each time when the loop is iterated. 
• These three sections are separated with semicolons.
• The for loop executes continuously until the assigned condition remains true. Once the given condition becomes false, control is shifted to the statement following the for.

Example:

Output:

While Loop

• The while loop is Java’s most common looping statement. 
• The statements inside the while loop will keep executing as long as the Boolean expression evaluates to true.
• Each execution is called an iteration.
• When the Boolean expression does not satisfy, control passes to the next line of code immediately following the loop.
• If the condition never becomes false, i.e., the condition is always true, then the while loop keeps getting executed. Such type of loop is known as an infinite loop.

Example

Output:

do while loop

• do-while loop won’t test the loop condition at the top of the loop; it checks the condition of the Boolean expression at the bottom of the loop to execute the statements inside the block at least once.
• This indicates that the do-while loop always executes at least once.
• After executing once, statements inside the do-while loop will keep executing as long as the Boolean expression evaluates to true.
            Syntax:
                    do {
                                    statement;
                         }
                    while(condition);

• Although the curly braces are not essential when only one statement is present, they are usually used to avoid confusion (to you, not the compiler) with the while.
• The do-while loop iterates continuously until the condition becomes false.

Example:

Output:  

Unconditional Statements

break statement

   In Java language, the break statement holds three uses. 

(1) As we have already seen, it terminates a statement sequence in a switch statement. 

(2) It is used to exit from a loop. 

(3) it is used as a “civilized” form of a goto statement. 

Let’s see the last two uses.

Using a break statement to exit from a loop:

• A break statement can be used to make immediate termination of a loop bypassing the normal loop conditional test.
• The loop is immediately terminated when the break statement is present inside the loop, and program control is transferred to the statement following it.

Example:

Output:

Using break as a form of Goto:

• The break statement in Java can also be used to give a “civilized” form of the goto statement.
• Java language does not have the goto statement.
• The goto statement can be useful when we are exiting from a deeply nested set of loops. To handle such a situation, Java provides an expanded form of the break statement.
• By using this form of break, we can break out of one or more blocks of the code. 
• These blocks need not be present in a loop or a switch. They can be any block.
• This kind of break works with a label. As we will see, break provides us with the benefits of a goto without its problems.

          General form:

                  break label;

Example:

Output:

Switch Statement

• The switch statement is a multiple-choice decision-making statement. 
• It is used to execute different cases based on equality.
• It provides a better alternative than a series of if-else-if statements. 
• It tests the value of an expression successively from a character constant or a list of integers.
•  When a match is found, then the statements associated with that constant are executed. 

          Syntax:
                  switch (expression)
                  {
                           case constant1:
                           statement
                           break;
                           case constant2
                           statement 
                           break; 
                           case constant3: 
                           statement 
                           break;
                           .
                           .
                           .
                          default
                          statement 
                  }

• The expression can be a character or an integer value, although floating-point expressions are not allowed.
• The value of an expression is tested with the constant values, one after the other, specified   within the case statements. 
• When a match is found, then the statement sequence associated with that particular case is executed, and it continues till the end of the switch, or a break statement is reached.
• The default statement is executed at the end if no matches are detected.
• The break statement is used under the switch statement. When a break statement is found, then the execution branches to the initial line of code that follows the whole switch statement.
•  The break statement is used to “jump out” of the switch.

Example:

Output:

Continue statement

• Sometimes it is helpful to force an early iteration of a loop.
• Using a continue statement in a while and do-while loop makes the control be shifted immediately to the conditional expression that controls the loop.
• The continue statement works somewhat similar to the break statement, but the continue statement forces the next iteration of the loop to take place instead of forcing termination.

• It is generally used when we want to skip a particular part of code for some condition. 

          Syntax:
                  //statements of the loop  
                  continue;  
                  //some particular lines of the code which we want to skip  

Example:

Output: