Computer Science Department FTSM Control Structure: Selection (Part 2) Knowledge: Understand various concepts of selection control structure Skill: Be.

Computer Science Department FTSMFTSM

Control Structure: Control Structure: SelectionSelection(Part 2)(Part 2)

Knowledge:Understand various concepts of selection control structure

Skill:Be able to develop a program containing selection control structure

TK1913-C ProgrammingTK1913-C Programming 22

ifif StatementsStatements

ifif

if - elseif - else

if – else - ifif – else - if


ifif StatementStatementThe structure is similar to single selection (flowchart)

Syntax:if (expression)if (expression)

statement;statement;or

if (expression) {if (expression) {statement1;statement1;statement2;statement2;

}}




}}

Don’t forget the Don’t forget the curly brackets !!curly brackets !!

Don’t forget the Don’t forget the brackets !!brackets !!


ifif StatementStatementThe similarity between single selection structure and

ifif statement:

Single Selection:if <condition is true> start

step 1

step 2

…

step k

end_if

Single Selection:if <condition is true> start

step 1

step 2

…

step k

end_if

if Statement:

if (<condition>) {

statement 1

statement 2

…statement k

}

if Statement:

if (<condition>) {

statement 1

statement 2

…statement k

}


ifif Statement Statement Example:int num1, num2, min;printf(“Key-in 2 numbers: “);scanf(“%d%d”, &num1, &num2);min = num1;if (num1 > num2)

min = num2;printf(“Smallest: %d\n”, min);

Example:int num1, num2, min;printf(“Key-in 2 numbers: “);scanf(“%d%d”, &num1, &num2);min = num1;if (num1 > num2)

min = num2;printf(“Smallest: %d\n”, min);

Key-in 2 numbers: _

num2 ?

num1 ?

min ?

Key-in 2 numbers: 20 15

_

20

15

2015

Key-in 2 numbers: 20 15

Smallest: 15

_

20 > 15?20 > 15?


ifif Statement Statement Example:int mark;

printf(“Mark: “);

scanf(“%d”, &mark);

if (mark > 80) {

printf(“Category: Excellent\n”);

printf(“Congratulations!”);

}

Example:int mark;



if (mark > 80) {

printf(“Category: Excellent\n”);

printf(“Congratulations!”);

}

Mark: _

mark ?92 > 80?92 > 80? 92

Mark: 92

_

Mark: 92

Category: Excellent

Mark: 92

Category: Excellent

Congratulations!


ifif Statement StatementExample:void main() {

int mark;



if (mark >= 50)

printf(“Pass\n”);

printf(“Your mark is %d”, mark);}

Example:void main() {

int mark;



if (mark >= 50)



What will the output What will the output be if the mark is 65?be if the mark is 65?


ifif Statement StatementExample:void main() {

int mark;



if (mark >= 50)

printf(“Pass\n”);printf(“Your mark is %d”, mark);

}


int mark;



if (mark >= 50)

printf(“Pass\n”);printf(“Your mark is %d”, mark);

}



if - elseif - else StatementStatementThe structure is similar to double selection (flowchart)


statement;statement;elseelse



} else} elsestatement3;statement3;





} else} elsestatement3;statement3;


if - elseif - else StatementStatement

orif (expression) {if (expression) {

statement1;statement1;statement2;statement2;

} else {} else {statement3;statement3;statement4;statement4;

}}

orif (expression) {if (expression) {

statement1;statement1;statement2;statement2;

} else {} else {statement3;statement3;statement4;statement4;

}}


if – elseif – else StatementStatementThe similarity between double selection structure and if - elseif - else statement:

Double Selection:if <condition is true> start

step 1…step k

end_ifelse start

step 1…step n

end_else

Double Selection:if <condition is true> start

step 1…step k

end_ifelse start

step 1…step n

end_else

if Statement:if <condition> {

statement 1…statement k

}else {

statement 1…statement n

}

if Statement:if <condition> {

statement 1…statement k

}else {

statement 1…statement n

}


if - elseif - else Statement Statement Example:if (num1 < num2)

min = num1;

else

min = num2;

printf(“Smallest: %d\n”, min);

Example:if (num1 < num2)

min = num1;

else

min = num2;


num2 15

num1 10

min ?

10 < 15?10 < 15?

_

10

Smallest: 10

_


if - elseif - else Statement Statement Example:if (num1 < num2)

min = num1;

else

min = num2;


Example:if (num1 < num2)

min = num1;

else

min = num2;


num2 15

num1 20

min ?

20 < 15?20 < 15?

_

15

Smallest: 15

_


if - elseif - else Statement Statement Example:if (num1 < num2) {

min = num1;max = num2;

}else {


}printf(“Min = %d, Max = %d\n”, min, max);

Example:if (num1 < num2) {


}else {


}printf(“Min = %d, Max = %d\n”, min, max);

num2 125

num1 700

min ??

700 < 125?700 < 125?

_

max ??

Min = 125, Max = 700

_

125

700


if – else if – else StatementStatementExample:void main() {

int mark;

printf(“Mark: “);scanf(“%d”, &mark);if (mark >= 50)

printf(“Pass\n”);else

printf(“Fail\n”);printf(“Your mark is %d”, mark);

}


int mark;




}





int mark;




}


int mark;




}





int mark;printf(“Mark: “);scanf(“%d”, &mark);if (mark >= 50)

printf(“Pass\n”);else {


}}



printf(“Pass\n”);else {


}}




Take a break ….Take a break ….

Why we need program Why we need program styles?….To ensure styles?….To ensure your program is your program is readable. Let’s look readable. Let’s look some examples..some examples..

Let’s have a minute break. Let’s have a minute break. While you’re having a break, While you’re having a break, let me introduce you some let me introduce you some program styles…..program styles…..


Take a break … (Learn styles)Take a break … (Learn styles)Example:void main() {



else printf(“Fail\n”);








Take a break … (Learn styles)Take a break … (Learn styles)Example:void main() {

int mark;printf(“Mark: “);scanf(“%d”, &mark);if (mark >= 50)printf(“Pass\n”);




int mark;printf(“Mark: “);scanf(“%d”, &mark);if (mark >= 50)printf(“Pass\n”);



Difficult to read!!!Difficult to read!!!Don’t you think Don’t you think so??so??



statement;statement;



if statementif statement

Let’s recap …Let’s recap …


statement;statement;else else



statement;statement;else else


if-else statementif-else statement

Ok now, let’s look at Ok now, let’s look at if – else –ifif – else –if statement statement


if – else - if if – else - if StatementStatement


statement;statement;else if (expression)else if (expression)





if-else-if statementif-else-if statementSyntax:

if (expression)if (expression)statement;statement;

else if (expression)else if (expression)statement;statement;

else if (expression)else if (expression)statement;statement;

elseelsestatement;statement;






if-else-if statementif-else-if statement


if – else - if if – else - if StatementStatement




statement;statement;else else (expression)(expression)





statement;statement;else else (expression)(expression)


if-else-if statementif-else-if statement

Be careful…common Be careful…common mistake made by mistake made by

students !!students !!


Let’s recap …Let’s recap …Example:

if <condition_1 is true> startstep m…

end_ifif <condition_2 is true> start

step n…

end_ifelse start

step x…

end_else

Example:if <condition_1 is true> start

step m…


step n…

end_ifelse start

step x…

end_else

Multiple SelectionMultiple Selection

Assume condition 1 is Assume condition 1 is true, so …true, so …

step m, step …. will be step m, step …. will be executedexecuted





step n…

end_ifelse start

step x…

end_else


step m…


step n…

end_ifelse start

step x…

end_else


Assume condition 1 is Assume condition 1 is false, so …false, so …

• step m, step …. will be step m, step …. will be skipped, and skipped, and

• condition 2 will be testedcondition 2 will be tested





step n…

end_ifelse start

step x…

end_else


step m…


step n…

end_ifelse start

step x…

end_else


Assume condition 2 is Assume condition 2 is true, so …true, so …

step n, step …. will be step n, step …. will be executedexecuted





step n…

end_ifelse start

step x…

end_else


step m…


step n…

end_ifelse start

step x…

end_else


Assume condition 2 is also Assume condition 2 is also false, so …false, so …

• step n, step …. will be step n, step …. will be skipped, and skipped, and

• step x will be executedstep x will be executed


Multiple Selection in CMultiple Selection in CExample:

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

char letter;

scanf(“%c”, &letter);if (letter >= ‘a’ && letter <= ‘z’ )

printf(“Lower case\n”);else if (letter >= ‘A’ && letter <= ‘Z’)

printf(“Upper case\n”);else if (letter >= ‘0’ && letter <= ‘9’)

printf(“Digit\n”);else

printf(“Special character\n”);}

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

char letter;






Is the letter a lower case? Is the letter a lower case?

Is the letter an upper case? Is the letter an upper case?

Is the letter a digit? Is the letter a digit?


Multiple Selection in CMultiple Selection in CExample:

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

char letter;






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

char letter;






(the letter is a lower case) (the letter is a lower case) truetrue

(the letter is a lower case) (the letter is a lower case) falsefalse(the letter is an upper case) (the letter is an upper case) truetrue(the letter is a lower case) (the letter is a lower case) falsefalse

(the letter is an upper case) (the letter is an upper case) falsefalse(the letter is a digit) (the letter is a digit) truetrue

(the letter is a lower case) (the letter is a lower case) falsefalse(the letter is an upper case) (the letter is an upper case) falsefalse

(the letter is a digit) (the letter is a digit) falsefalse


ExerciseExerciseDevelop a program for the following problem.

Given a mark, determine its grade based on the table below:

74 < mark < 100 grade = A64 < mark < 75 grade = B54 < mark < 65 grade = C39 < mark < 55 grade = D 0 < mark < 40 grade = E others error message


AAnnsswweerr11

int mark;printf(“Key-in the mark: “);scanf(“%d”,&mark);if ((mark >= 75) && (mark <= 100))

printf("Grade = A”);else if ((mark >= 65) && (mark <= 74))

printf(" Grade = B”); else if ((mark >= 55) && (mark <= 64))

printf(" Grade = C”);else if ((mark >= 40) && (mark <= 54))

printf(" Grade = D”);else if ((mark >= 0) && (mark <= 39))

printf(" Grade = E”);else

printf(“Input error\n”);


int mark;char grade ;printf(“Key-in the mark : “);scanf(“%d”,&mark);if ((mark >= 75) && (mark <= 100))

grade =‘A’;else if ((mark >= 65) && (mark <= 74))

grade =‘B’; else if ((mark >= 55) && (mark <= 64))

grade =‘C’;else if ((mark >= 40) && (mark <= 54))

grade =‘D’;else if ((mark >= 0) && (mark <= 39))

grade =‘E’;else

printf(“Input error\n”);printf(“Your grade is %c”, grade );

AAnnsswweerr22


int mark;char grade;printf(“Key-in the mark: “);scanf(“%d”,&mark);if ((mark >= 75) && (mark <= 100))

grade=‘A’;else if ((mark >= 65) && (mark <= 74))

grade=‘B’; else if ((mark >= 55) && (mark <= 64))

grade=‘C’;else if ((mark >= 40) && (mark <= 54))

grade=‘D’;else if ((mark >= 0) && (mark <= 39))

grade=‘E’;if ((mark > 100) || (mark < 0))

printf(“Input error\n”);else

printf(“Your grade is %c”, grade);

AAnnsswweerr33


Nested Nested ififss

ifif statement that contains other ifif / if - elseif - else statements


Nested Nested ififssExample:if (age > 18) {

if (age > 55) price = 2.50; /* Price for senior citizens */

elseprice = 5.00; /* Price for adults */

}else {

if (age < 1)price = 0.0; /* Price for infants */

elseprice = 1.50; /* for children & teenagers*/

}

Example:if (age > 18) {



}else {

if (age < 1)price = 0.0; /* Price for infants */

elseprice = 1.50; /* for children & teenagers*/

}

This price is valid for This price is valid for people: age > 55people: age > 55

This price is valid for This price is valid for people: 18 < age < 55people: 18 < age < 55

This price is valid for This price is valid for people: age < 1people: age < 1

This price is valid for This price is valid for people: 1 < age < 18people: 1 < age < 18


Nested Nested ififs - Problems - ProblemExample:if (age > 18)



Example:if (age > 18)



Which Which ifif does this does this elseelse belong to? belong to?


Nested Nested ififs - Problems - Problem

if (age > 18) {

if (age > 55)

price = 2.50;

else

price = 5.00;

}

if (age > 18) {

if (age > 55)

price = 2.50;

else

price = 5.00;

}

if (age > 18) {

if (age > 55)

price = 2.50;

}

else

price = 5.00;

if (age > 18) {

if (age > 55)

price = 2.50;

}

else

price = 5.00;

Which one?


Nested Nested ififs - Problems - ProblemBy default, elseelse will be attached to the nearest ifif

if (age > 18)

if (age > 55)

price = 2.50;

else

price = 5.00;

if (age > 18)

if (age > 55)

price = 2.50;

else

price = 5.00;

if (age > 18) {

if (age > 55)

price = 2.50;

else

price = 5.00;

}

if (age > 18) {

if (age > 55)

price = 2.50;

else

price = 5.00;

}


switchswitch and and breakbreak The structure is similar to multiple selection (flowchart)

Syntax:switch (expression) {switch (expression) {case expression1:case expression1:

statement1;statement1;break;break;

case espression2:case espression2:statement2;statement2;break;break;

……default:default:

expressionX;expressionX;break;break;

}}

Syntax:switch (expression) {switch (expression) {case expression1:case expression1:

statement1;statement1;break;break;

case espression2:case espression2:statement2;statement2;break;break;

……default:default:


}}

Syntax:switchswitch (expression) { (expression) {

casecase expression1: expression1:statement1;statement1;break;break;

casecase espression2: espression2:statement2;statement2;break;break;

……defaultdefault::


}}






}}

Don’t forget the Don’t forget the brackets !!brackets !!

Don’t forget the Don’t forget the curly brackets !!curly brackets !!Don’t forget the Don’t forget the

colons !!colons !!


switchswitch and and breakbreak Important Rule !!






}}






}}

Must be Must be INTEGER or INTEGER or

CHAR !CHAR !


switchswitch and and breakbreakExample: switch (month) {

case 1:printf(“January\n”);break;

case 2:printf(“February\n”);break;

case 3:printf(“March\n”);break;

default:printf(“Others\n”);break;

} printf(“End”);

Example: switch (month) {case 1:

printf(“January\n”);break;





Assume month = 1, Assume month = 1, so …so …

……this step will be this step will be executed. Later …executed. Later ………casecase is terminated is terminated here. Jump to …here. Jump to …

January

_

January

End _














……this step will be this step will be executed. Later …executed. Later …

March

_

March

End _


……casecase is terminated is terminated here. Jump to …here. Jump to …







}printf(“End”);






}printf(“End”);

Now…what will Now…what will happen if this happen if this breakbreak is taken out from the is taken out from the

program?program?



case 2:printf(“February\n”);










No more !!No more !!














……this step will be this step will be executed. Later …executed. Later …

February

_

February

March

_


……casecase is terminated is terminated here. Jump to …here. Jump to …

February

March

End _

……execution continues. Thus, execution continues. Thus, this step is executed . So …this step is executed . So …














Now…what will Now…what will happen if these happen if these

breakbreaks are taken out s are taken out from the program?from the program?

And … And … if month = 1 ?if month = 1 ?And … And … if month = 34 ?if month = 34 ?


ExerciseExercise

To practice what you’ve learned, try exercises on page …

/* Do exercises from pg 155 -156 of Pengaturcaraan C


End of Lecture 7 (Part 2)End of Lecture 7 (Part 2)

At last, chap 7 is At last, chap 7 is finished. What’s next??? finished. What’s next???

Control Structure: RepetitionControl Structure: Repetition on on the way… the way…

Computer Science Department FTSM Control Structure: Selection (Part 2) Knowledge: Understand various concepts of selection control structure Skill: Be.

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