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Flow of controls

Unit :3

Part-1

(decision control statements)

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Syllabus-part1

1. compound statements(blocks).

2. Decision control statement:-

1. if statement.

2. if-else statement.

3. nested if-else.

4. else if ladder.

5. switch statement.

6. goto statement.

7. conditional operators.

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compound statements(blocks)

A block of statements, also called as

compound statement, is a group of

statements that is treated by the compiler as a

single statement. Blocks begin with a brace bracket { and ends

also close with a }. Block can be used any

place where a single statement is allowed.

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Decision Control Statements

C++ language is able to perform different sets of

actions depending on the circumstances. The threemajor decision making instructions are :-

The If Statements

If-else Statements

The Switch Statements

Many times, we want a set of Instructions to beexecuted in one situation, and an entirely different

set of instructions to be executed in another

situation.This kind of situation is done in C

programs using decision control Instruction.

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Conditions

Conditions are expressions that evaluate to

a booleanvalue atrue or false value(trueandfalseare C++ keywords, representing

the two possible values of a boolean

expression or variable). Simple conditionsinvolve two operands, each of which can be a

variable or a literal value, and an operator,

typically a comparison operator.

For ex: to check a is greater than and equal to

b we can writr the conditio as:- if(a>=b).

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Composite Conditions

Very often, we encounter situations where the condition

can not be expressed as the simple conditions from theprevious section, just by comparing two values. An exampleof such situations is testing if a number is within agiven rangeof values; for instance, testing if a number isbetween 0 and 10.

This example involves testing twoconditions, and verifyingif the two conditions are simultaneously met. In otherwords, we want to test if the number is greater than orequal to 0 andalso less than or equal to 10.

To this end, we use logical operators to combine two

conditions. In the above example, we use the logicalAND operator &&, as shown below:

For ex: if (0>= number && number

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Decision Control Statements

1. The if Statement.2. The if-else Statement.

3. The Nested if-else.

4. else-if ladder

5. The switch statement.

6. The conditional operators.

7. The go to statement.

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1. The if Statement.

The general syntax:

If(test condition)

{

Statement -block1;

Statement -block2;

----------;

----------;}

Statement-x;

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The if Statement.contd

If the condition returns true value the all thestatements inside the brace of if block are

executed.otherwise,if the condition return

false, then the statement outside the if block

is executed.

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2. Ifelse statement

The simple ifstatement covers the cases

where we have a fragment of code that should

be executed depending on a condition. If we

have a situation where we have two possible

actions, and we want to do one or the other,

depending on a given condition, we use

the if elsestatement.

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Ifelse statementcontd

The general syntax:

If(test condition)

{

statement-block1;

}

Else

{

statement-block2;

}

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3. Nesting of if and Ifelse statement

The if-else statement allows a choice to be made

between two possible alternatives. Sometimes a

choice must be made between more than two

possibilities. Which ca be achieved by usingnested if block and nested if-else block.

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Nested if statement

The General syntax:

If (condition1)

{

if (condition2)

{

statement(s);

}

}

Statement-x.

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Nested if statement..contd

If the condition1 is true than only the outer if

body will execute to check the condition2

otherwise statement-x will get executed.

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Nested Ifelse statement..contdIf(test condition 1)

{

If(test condition 2)

{

statement-block-1;

}Else

{

statement-block-2;

}Else

{

statementblock-3;

}

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Nested Ifelse statement.contd

If the test expression is true, it will execute the

code before else part but, if it is false, the

control of the program jumps to the else part

and check test expression 1 and the processcontinues. If all the test expression are false

then, the last statement is executed

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4. else If statement

An extension of the nesting of if else is

the else ifstatement. What the nested if-else

can do is can be done byelse if statement.

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else If statement..contdThe general syntax

if (condition 1){

// block 1}else if (condition 2){

// block 2}...else if (condition N){

// block N

}else{

// Optional block to be executed if all of the// previous conditions evaluated to false

}

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In case of else if only oneof the blocks will be

executed. This includes the blockcorresponding to the optional elsepart

ifone of the previous blocks executes, then

the rest is skipped, and execution continuesafter the end of the elseblock, or after the

last else ifblock, in the cases where there is

no else.

else If statement..contd

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5. Switch case:

The switchstatement provides a convenient

mechanism to execute one out of several

possible fragments of code, depending on the

value of an integral variable or expression.

A typical example that illustrates the use of

the switchstatement is handling a menu

selection.

S it h td

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Switch case..contd:

Switch(integer expression/char expression)

{case cont-1:

statement-block1;

Break;

-------------------;

-------------------;

default:

statement-block;Break;

}

Statement-a;

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Goto statement

A gotostatement provides an unconditional

jump from the goto to a labeled statement in

the same function.

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Goto statement

Goto label;

-----------------;

-----------------;

Label:Statement-1;

statement-2;

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Goto statement..contd

Where labelis an identifier that identifies a

labeled statement. A labeled statement is any

statement that is preceded by an identifier

followed by a colon (:).

Use of gotostatement is highly discouraged

because it makes difficult to trace the control

flow of a program, making the program hardto understand and hard to modify.

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The Conditional Operators(ternary operator):

The conditional operators ? And : are sometimes calledTernary Operators, since they take three arguments.Their

general form is:

Expression 1 ? Expression 2 : Expression 3

ie.

condition ?value_if_true :value_if_false

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The end of part-1