COMPUTERPROGRAMMINGDAE 20102

CHAPTER 5PROGRAM CONTROL

INTRODUCTION

• Control Structures=control the flow of execution in a program or function

• There are 3 control structures:-▫ Sequence structure▫ Selection structure▫ Repetition structure

INTRODUCTIONTypes of selection structure:-i. if-selection (single-selection)=selects/perform an

action if a condition is true or skips the action if the condition is false

ii. If-else selection (double-selection)=performs an action if a condition is true and performs a different action if condition is false

iii. Switch selection (multiple-selection)=performs one of many different actions depending on the value of an expression

CONDITION

•Relational and Equality Operators

Operator Meaning Type

< Less than Relational

> Greater than Relational

<= Less than or equal to Relational

>= Greater than or equal to

Relational

== Equal to Equality

!= Not equal to Equality

CONDITION•Operator Precedence

Operator PrecedenceFunctions calls Highest

Lowest

! + - & (unary operators)

* / %

+ -

< <= >= >

== !=

&&

| |

=

The if Selection Structure•Used to choose among alternative courses

of action•If the algorithm/flow chart have a diamond

symbols, then it will used control structures•Example: The pseudo-code statement

If student’s grade is greater than or equal to 55print “passed”

if (grade>=55)printf (“Passed\n”);

The if Selection Structure•Flowchart of the preceding if statement

Grade >=55 printf (“passed”)True

False

End

Sel

ectio

n S

truc

ture

The if Selection Structure

Notice that C uses == to test for equality, while it uses = to assign a value to a variable.

The if-else Selection Structure•Performs an indicated action when the

condition is true; otherwise the action is skipped

•Pseudo-code statement:-

if student’s grade is greater than or equal to 55

print “passed”else

print “failed”

The if-else Selection Structure•Syntax for if-else selection:-

if (condition){

statement T;}else{

statement F;}

if (result>=55){

printf(“Passed\n”);printf(“Congratulations\n”);

}else{

printf(“Failed\n”);ptintf(“Good luck in the resits\n”);

}

Compound Statement

The if-else Selection Structure•Syntax for multi way decision based on

several conditions:-

if (condition 1)statement 1;

else if (condition 2)statement 2;

else if (condition n)statement n;

elsestatement a;

if (result>=80)printf(“Passed: Grade A\n”);

else if (result>=70)printf(“Passed: Grade B\n”);

else if (result>=55)printf(“Passed: Grade C\n”);

elseprintf(“Failed\n”);

The Nested if-else Selection Structure

• if-else statement may contain any single or compound statement including another if-else statement

if (hours > 40)if (hours >60)

printf(“double time”);else

printf(“time is half”); if (hours > 40)if (hours >60)

printf(“double time”);else

printf(“time is half”);

Which if statement should be paired with else statement

The Nested if-else Selection Structure

•Braces can be used to change the matching above

if (hours > 40) {if (hours >60)

printf(“double time”);}

else printf(“time is half”);

The Nested if-else Selection Structure

•Exampleif (road_status==0) if (temp>0) {

printf(“Wet roads ahead\n”);

printf(“Stopping time doubled\n”); } else {

printf(“Icy roads ahead\n”); printf(“Stopping time quadrupled\n”);

}else

printf(“Drive carefully!\n”);

road_status is ‘s’

Temp>0

Drive carefully message

Icy road message

True

False False

True

The switch statement• Alternative to the if-else chain• Compared the value of an integer expression to a

specific value in order to select a set of instructions to be executed from many possible alternatives

• Also another form of multi-way decision, but can only be used in certain cases where:-

▫ If only 1 variable is tested, all branches must depend on the value of that variable. Variable must be of an integral type (int ,long, short or char)

▫ Each possible value of the variable can control a single branch. A final, catch all, default branch may optionally used to trap unspecified cases

The switch statement•General syntax of switch

statementswitch (expression){case value_1;

statement A;statement B;break;

case value_2;statement C;statement D;break;

case value_n;statement Y;statement Z;break;

default;statement W;statement X;

}

• Break statement is used to exit from a loop or a switch

• With loops, break can be used to force an early exit from the loop or to implement a loop with a test to exit in the middle of the loop body

The continue Statement•Similar to break but encountered less

frequently•Only works within loops where its effect is

to force an immediate jump to the loop control statement

The goto Statement•goto loop construct uses two elements; first

is a label and second is colon (:).•A label marks a location within a program to

which program execution can jump•Label must be identifiers•Normally the goto statement is executed if

some logical test is true•goto statement can be avoided by using

return, break or continue statement•goto statement generally considered bad

programming practices

The goto Statement•goto coding

example#include<stdio.h>int main (){

int count=1;mula:

if (count>10)goto akhir;

printf ("%d",count);++count;goto mula;

akhir:printf("Akhir/n");

return 0;}

Label

Label

Looping Statement•There are three types of looping statement

in C:-▫for statement▫do…while statement▫while statement

for Statement• There are three loop control components

▫ Initialization of the loop control variable▫ Test of the loop repetition condition, and▫ Change (update) of the loop control variable

• Syntax format for (initialization expression;

loop repetition condition; update expression) statement

• Examplefor (count_star=0;count_star <N;count_star+=1)

printf(“*”);

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#include<stdio.h>#define CBEGIN 10#define CLIMIT -5#define CSTEP 5

int main (void){

int celcius;double fahrenheit;printf(“ Celcius Fahrenheit”\n);

for (celcius = CBEGIN;celcius >= CLIMIT;celcius -= CSTEP)

{fahrenheit = 1.8 * celcius + 32.0;printf(“%6c%3d%8c%7.2f\n”, ‘ ‘,celcius, ‘

‘,fahrenheit);}return (0);

}

for Statement

do..while Statement

•Both the for statement and the while statement evaluate a loop repetition condition before the first evaluation of the loop body

•do..while statement evaluate on the pretest desire then do the looping

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do..while Statement•Syntax

dostatement

while (loop repetition condition);•Exampledostatus = scanf (“%d”,&num);

while (status!=0);

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while Statement•Syntax Format

while (loop repetition condition)statement

•Examplecount_star = 0;while (count_star < N) {printf (“*”);count_star = count_star+1;

}

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Programming C

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Programming C

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Programming C

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Programming C

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Programming C

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