P6 Control Structures

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Control StructuresControl Structures

Used to control the execution of various

statements in the program.

By default, instructions in the program areexecuted sequentially.

It is classified into three categories.Decision Making

Loops

Case


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Decision MakingDecision Making

When we want a set of instruction to be

executed at one situation, and entirely

different set of instruction to be executedin another situation.

Implemented using the following:The ifstatement

The if-else statement

The conditional operators


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ififstatementstatement

General form ofifstatement is:

if ( this condition is true )

{

statement 1;

statement 2;

.

.statement n;

}


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IfIfstatementstatement--exampleexample

main( )

{

int num ;

printf ( "Enter a number less than 10 " ) ;

scanf ( "%d", &num ) ;

if ( num


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IfIf--elseelse statementstatement

Ifstatement does nothing when the expressionevaluates to false.

General form ofif-else statement:

if(expression)

{

statements;

}

else

{

statements;

}


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IfIf--elseelse statement examplestatement example

if(A>B)

{

printf(A is big);

}else

{

printf(B is big)

}

If-else statements can also be nested


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Logical operatorsLogical operators

C allows use of logical operators.

AND &&

OR ||NOT !


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Logical OperatorsLogical Operatorsmain( )

{

int m1, m2, m3, m4, m5, per ;

printf ( "Enter marks in five subjects " ) ;

scanf ( "%d %d %d %d %d", &m1, &m2, &m3, &m4, &m5 ) ;

per = ( m1 + m2 + m3 + m4 + m5 ) / 5 ;

if ( per >= 60 )

printf ( "First division" ) ;

if ( ( per >= 50 ) && ( per < 60 ) )

printf ( "Second division" ) ;

if ( ( per >= 40 ) && ( per < 50 ) )

printf ( "Third division" ) ;if ( per < 40 )

printf ( "Fail" ) ;

}


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Logical OperatorsLogical Operators

! Operator Reverses the result of the

operator it operates on.

For example, if the expression evaluatesto non-zero, then by applying ! Operator

we can make it it zero and vice-versa.

Along with the hierarchy of other

operators, logical operators also has a

priority which is mentioned in the table.


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Hierarchy of logical operatorsHierarchy of logical operators

Note: In C assignment operator = is, different from relational operator ==.


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Conditional or ternary operatorConditional or ternary operator

Conditional operators ? And : are called

ternary operators,since they take three

arguments.

General form of ternary operator is:

Expression1?expression2:expression3

If expression 1 is true,value returned isexpression2,else expression 3 will be

returned.


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Ternary operatorsTernary operators--ExampleExample

int x, y ;

scanf ( "%d", &x ) ;

y = ( x > 5 ? 3 : 4 ) ;

Equivalent if statement will beif ( x > 5 )

y = 3 ;

else

y=4;


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LoopsLoops

Used to perform set of operations

repeatedly.

Three statements are used to achievelooping

While statement

For statement

Do-while statement


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While statementWhile statement

General form of while statement

initialize loop counter

while(test loop counter for a condition)

{statement 1;

statement 2;

..

..

statement n;

increment or decrement loop counter;

}


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While statement exampleWhile statement example

main()

{

int i=1;

while(i


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Increment and Decrement operatorIncrement and Decrement operator

++ operator is used to increment the value by 1.

i=i+1 => i++;

-- operator is used to decrement the value by 1.

i=i-1 => i--;

Similarly, compound assignment += operator can

be used.

j+=10 => j=j+10


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Increment operatorIncrement operator

Consider the statement:While(i++


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forforlooploop

This is one of the commonly used looping

statement in C.

General form of for statement:for(initialize counter; test counter; increment counter)

{

Statements;

}


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forforlooploop

It allows us to specify three things in a

single line.Setting a loop counter to an initial value

Testing a loop counter to determine whether it has

reached number of repetitions

Increase the loop counter each time when the

program segment within the loop has been

executed


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forforlooploop

main( )

{

int i ;

for ( i = 1 ; i


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dodo--whilewhile looploop

When you are not sure about how many times

the loops has to be executed.

General form of do-while statement is:

do

{

statements;

}while(condition)Here statements inside the loop is getting

executed at least once.


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dodo--whilewhile looploop--exampleexample

main( )

{

char another ;

int num ; do

{

printf ( "Enter a number " ) ;

scanf ( "%d", &num ) ;

printf ( "square of %d is %d", num, num * num ) ;

printf ( "\n Want to enter another number y /n " ) ;scanf ( " %c", &another ) ;

} while ( another == 'y' ) ;

}


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Break statementBreak statement

Used to jump out of the loop instantly.

Control is passed to the first statement

after the loop. This statement is used with for and while

loopswhile ( j++


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Continue statementContinue statement

To take the control to the beginning of the

loop and bypassing the statements inside

the loop.for ( i = 1 ; i


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goto statementgoto statement

Used to transfer the control to anywhere in

the program.

General form of goto isgoto label;

..

..label:


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Switch statementSwitch statement

This allows us to make a decision from thenumber of choices.

It is also called switch-case default.

General form of switch statement isswitch ( integer expression )

{

case constant 1 :

do this ;

case constant 2 :

do this ;case constant 3 :

do this ;

default :

do this ;

}


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Switch statementSwitch statement--exampleexample

main( )

{

int i = 2 ;

switch ( i )

{

case 1 :

printf ( "I am in case 1 \n" ) ;case 2 :

printf ( "I am in case 2 \n" ) ;

case 3 :

printf ( "I am in case 3 \n" ) ;

default :

printf ( "I am in default \n" ) ;

}}


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P6 Control Structures

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