Control Statements in C programming

8/11/2019 Control Statements in C programming

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CONTROL STATEMENTS

Lakhbir Singh(Lect.IT)

S.R.S.G.P.C.G. Ludhiana


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Flow of Control

Unless specified otherwise, the order ofstatement execution through a function is

linear: one statement after another in

sequence

Some programming statements allow us to:

decide whether or not to execute a particular

statement execute a statement over and over, repetitively

These decisions are based on boolean

expressions(or conditions) that evaluate to


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Conditional Statements A conditional statementlets us choose which statement

will be executed next

Therefore they are sometimes called selection statements

Conditional statements give us the power to make basicdecisions

The C conditional statements are the:

if statement if-else statement

switch statement


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Logic of an if statement

condition

evaluated

statement

true

false


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The if Statement

The if statementhas the following syntax:

if ( condition)statement;

ifis a Creserved word

The conditionmust be a

boolean expression. It must

evaluate to either true or false.

If the conditionis true the statementis executed.

If it is false the statementis skipped.


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Logic of an if-else statement

condition

evaluated

statement1

true false

statement2


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The if-else Statement

An else clausecan be added to an ifstatement to make an if-else statement

if ( condition)statement1;

elsestatement2;

If the conditionis true, statement1is executed;

if the condition is false, statement2is executed

One or the other will be executed, but not both


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Boolean Expressions

A condition often uses one of C's equality operators or relational

operators, which all return boolean results:

== equal to

!= not equal to greater than

= greater than or equal to

Note the difference between the equality operator (==) and the

assignment operator (=)


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Boolean Expressions in C

C does not have a boolean data type.

Therefore, C compares the values of variables and expressionsagainst 0 (zero) to determine if they are true or false.

If the value is 0 then the result is implicitly assumed to befalse.

If the value is different from 0 then the result is implicitlyassumed to be true.

C++ and Java have boolean data types.


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Block Statements

Several statements can be grouped together

into a block statement delimited by braces

A block statement can be used wherever astatement is called for in the C syntax rulesif (total > MAX)

{printf ("Error!!\n");errorCount++;

}


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Block Statements

In an if-elsestatement, the ifportion,or the elseportion, or both, could be block

statementsif (total > MAX){

printf("Error!!");errorCount++;}else{

printf ("Total: %d, total);

current = total*2;}


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Nested if Statements

The statement executed as a result of an ifstatement or

elseclause could be another ifstatement

These are called nested if statements

An else clause is matched to the last unmatched if(no

matter what the indentation implies)

Braces can be used to specify the ifstatement to which an

else clause belongs


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The switch Statement

The switch statementprovides another way to

decide which statement to execute next

The switch statement evaluates an expression,then attempts to match the result to one of

several possible cases

Each case contains a value and a list of

statements

The flow of control transfers to statement 2004 Pearson Addison-Wesley. All rights reserved


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Often a break statementis used as the last

statement in each case's statement list

A break statement causes control to transferto the end of the switch statement

If a break statement is not used, the flow of

control will continue into the next case

Sometimes this may be appropriate, but often

we want to execute only the statements


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switch (option){

case 'A':aCount++;

break;case 'B':bCount++;break;

case 'C':

cCount++;break;default:

otherCount++;break;

}

An example of a switch statement:


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The expression of a switchstatement must

result in an integral type, meaning an integer

(byte, short, int,) or a char

It cannot be a floating point value (floator

double)

The implicit test condition in a switch

statement is equality

You cannot perform relational checks with a


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The general syntax of a switchstatementis:

switch ( expression){

case value1:

statement-list1case value2:statement-list2

case value3:statement-list3

case ...

}

switch

and

case

are

reserved

words

If expressionmatches value2

control jumps

to here


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Repetition in Programs

In most software, the statements in theprogram may need to repeat for many times.

e.g., calculate the value of n!.

If n= 10000, its not elegant to write the code as1*2*3**10000.

Loopis a control structure that repeats a group

of steps in a program. Loop bodystands for the repeated statements.

There are three C loop control statements:

while, for, and do-while. 5-19


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Flow Diagram of Loop Choice Process

Copyright 2004 Pearson Addison-Wesley.All rights reserved.

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e.g., calculate the value of n!

e.g., read the content in a file


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Comparison of Loop Choices (1/2)

Kind When to Use C Structure

Counting loop We know how many loop

repetitions will be needed

in advance.

while, for

Sentinel-

controlled loop

Input of a list of data ended

by a special value

while, for

Endfile-controlled loop

Input of a list of data froma data file

while, for

5-21


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Comparison of Loop Choices (2/2)

Kind When to Use C Structure

Input validation

loop

Repeated interactive input

of a value until a desired

value is entered.

do-while

General

conditional

loop

Repeated processing of

data until a desired

condition is met.

while, for

5-22


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The while Statement in C

The syntax ofwhilestatement in C:while(loop repetition condition)

statement

Loop repetition conditionis the condition

which controls the loop.

The statementis repeated as long as the loop

repetition condition is true.

A loop is called an infinite loopif the loop

repetition condition is always true.5-23


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An Example of a whileLoop

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Statement

Loop repetition condition

Loop control variableis the variable whose value controls

loop repetition.

In this example, count_empis the loop control variable.


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Flowchart for a whileLoop

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Statement


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Compound Assignment Operators (1/2)

The loop body usually consists of statements

of the form: variable = variable op expression.

e.g., count_emp= count_emp+ 1;

C provides compound assignment operators

which enable a more concise notation for this

kind of statements.

variable op = expressionis the same to

variable = variable op expression.


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Compound Assignment Operators (2/2)

Simple AssignmentOperators

Compound AssignmentOperators

count_emp =

count_emp + 1;

count_emp += 1;

time = time -1; time -= 1;

product = product *

item;

product *= item;

total = total /

number;

total /= number;

n = n % (x+1); n %= x+1;

5-27


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The forStatement in C The syntax of

forstatement in C:

for(initialization expression;

loop repetition condition;

update expression)

statement

The initialization expressionset the initial value of the

loop control variable.

The loop repetition conditiontest the value of theloop control variable.

The update expressionupdate the loop control

variable. 5-28


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An Example of the forLoop

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Initialization Expression

Update Expression

count_empis set to 0 initially.

count_empshould not exceed the value of number_emp.

count_empis increased by one after each iteration.


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Comparison of Prefix and Postfix

Increments

Copyright 2004 Pearson Addison-Wesley.All rights reserved.

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The value of the expression (that uses the ++/-- operators)

depends on the position of the operator.

The valueof j is

increased

The value

of j is not

increased


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Nested Loops

Nested loops consist of an outer loopwith oneor more inner loops.

e.g.,

for (i=1;i


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An Example of the do-whileLoop

/* Find even number input */

do{printf(Enter a value: );

scanf(%d, &num);

}while(num % 2 !=0)

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This loop will repeat if the user

inputs odd number.

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Control Statements in C programming