1. Control Structure: Selection (Part 2)
Knowledge:
Understand various concepts of selection control structure
Skill:
Be able to develop a program containing selection control structure
FTSM
Computer Science Department

2. if Statements if
if – else - if
if - else
TK1913-C Programming

3. Don’t forget the brackets !! Don’t forget the curly brackets !!
if Statement
The structure is similar to single selection (flowchart)
Syntax:
if (expression)
statement; or
if (expression) {
statement1;
statement2; }
Don’t forget the brackets !!
Don’t forget the curly brackets !!
TK1913-C Programming

4. if Statement
The similarity between single selection structure and if statement:
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 }
TK1913-C Programming

5. if Statement 20 15 ? 20 > 15? 15 20 Example: num1 num2 min
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: 20 15 _ 20 15
num2 ?
num1
min
20 > 15? 15 20
Key-in 2 numbers: _
Key-in 2 numbers: 20 15
Smallest: 15 _
TK1913-C Programming

6. if Statement 92 > 80? 92 ? Example: mark int mark;
printf(“Mark: “);
scanf(“%d”, &mark);
if (mark > 80) {
printf(“Category: Excellent\n”);
printf(“Congratulations!”); }
92 > 80? 92
Mark: 92 _
mark ?
Mark: 92
Category: Excellent
Congratulations!
Mark: 92
Category: Excellent
Mark: _
TK1913-C Programming

7. if Statement Example: What will the output be if the mark is 65?
void main() {
int mark;
printf(“Mark: “);
scanf(“%d”, &mark);
if (mark >= 50)
printf(“Pass\n”);
printf(“Your mark is %d”, mark); }
What will the output be if the mark is 65?
TK1913-C Programming

8. if Statement Example: What will the output be if the mark is 35?
void main() {
int mark;
printf(“Mark: “);
scanf(“%d”, &mark);
if (mark >= 50)
printf(“Pass\n”);
printf(“Your mark is %d”, mark); }
What will the output be if the mark is 35?
TK1913-C Programming

9. if - else Statement
The structure is similar to double selection (flowchart)
Syntax:
if (expression)
statement;
else or
if (expression) {
statement1;
statement2;
} else
statement3;
TK1913-C Programming

10. if - else Statement or if (expression) { statement1; statement2;}
TK1913-C Programming

11. if – else Statement
The similarity between double selection structure and if - else statement:
Double Selection:
if <condition is true> start
step 1 …
step k
end_if
else start
step n
end_else
if Statement:
if <condition> {
statement 1 …
statement k }
else {
statement n
TK1913-C Programming

12. if - else Statement Example: 15 10 ? 10 < 15? 10
if (num1 < num2)
min = num1;
else
min = num2;
printf(“Smallest: %d\n”, min);
num2 15
num1 10
min ?
10 < 15? 10
Smallest: 10 _ _
TK1913-C Programming

13. if - else Statement Example: 15 20 ? 20 < 15? 15
if (num1 < num2)
min = num1;
else
min = num2;
printf(“Smallest: %d\n”, min);
num2 15
num1 20
min ?
20 < 15? 15
Smallest: 15 _ _
TK1913-C Programming

14. if - else Statement Example: 700 700 < 125? 125 ?? 125 ?? 700 num1
if (num1 < num2) {
min = num1;
max = num2; }
else {
min = num2;
max = num1;
printf(“Min = %d, Max = %d\n”, min, max);
num1
700
700 < 125?
num2
125
min ??
125
max ??
700 _
Min = 125, Max = 700 _
TK1913-C Programming

15. if – else Statement Example:
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); }
What will the output be if the mark is 21?
What will the output be if the mark is 74?
TK1913-C Programming

16. if – else Statement Example:
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); }
What will the output be if the mark is 74?
What will the output be if the mark is 14?
TK1913-C Programming

17. if – else Statement Example:
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); }
What will the output be if the mark is 14?
What will the output be if the mark is 70?
TK1913-C Programming

18. Take a break …. Let’s have a minute break.
While you’re having a break, let me introduce you some program styles…..
Why we need program styles?….To ensure your program is readable. Let’s look some examples..
TK1913-C Programming

19. Take a break … (Learn styles)
Example:
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); }
TK1913-C Programming

20. Take a break … (Learn styles)
Example:
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); }
Difficult to read!!!
Don’t you think so??
TK1913-C Programming

21. Let’s recap … Syntax: if (expression) statement; else
if-else statement
Syntax:
if (expression)
statement;
if statement
Ok now, let’s look at if – else –if statement
TK1913-C Programming

22. if – else - if Statement Syntax: if (expression) statement;
else if (expression)
else
if-else-if statement
Syntax:
if (expression)
statement;
else if (expression)
if-else-if statement
TK1913-C Programming

23. Be careful…common mistake made by students !!
if – else - if Statement
Syntax:
if (expression)
statement;
else if (expression)
else (expression)
if-else-if statement
Be careful…common mistake made by students !!
TK1913-C Programming

24. Assume condition 1 is true, so … step m, step …. will be executed
Let’s recap …
Example:
if <condition_1 is true> start
step m …
end_if
if <condition_2 is true> start
step n
else start
step x
end_else
Multiple Selection
Assume condition 1 is true, so …
step m, step …. will be executed
TK1913-C Programming

25. Assume condition 1 is false, so …
Let’s recap …
Example:
if <condition_1 is true> start
step m …
end_if
if <condition_2 is true> start
step n
else start
step x
end_else
Multiple Selection
Assume condition 1 is false, so …
step m, step …. will be skipped, and
condition 2 will be tested
TK1913-C Programming

26. Assume condition 2 is true, so … step n, step …. will be executed
Let’s recap …
Example:
if <condition_1 is true> start
step m …
end_if
if <condition_2 is true> start
step n
else start
step x
end_else
Multiple Selection
Assume condition 2 is true, so …
step n, step …. will be executed
TK1913-C Programming

27. Assume condition 2 is also false, so …
Let’s recap …
Example:
if <condition_1 is true> start
step m …
end_if
if <condition_2 is true> start
step n
else start
step x
end_else
Multiple Selection
Assume condition 2 is also false, so …
step n, step …. will be skipped, and
step x will be executed
TK1913-C Programming

28. Multiple Selection in C
Example:
#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”); }
Is the letter a lower case?
Is the letter an upper case?
Is the letter a digit?
TK1913-C Programming

29. Multiple Selection in C
Example:
#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”); }
(the letter is a lower case) true
(the letter is a lower case) false
(the letter is an upper case) false
(the letter is a digit) true
(the letter is a lower case) false
(the letter is an upper case) true
(the letter is a lower case) false
(the letter is an upper case) false
(the letter is a digit) false
TK1913-C Programming

30. Exercise Develop a program for the following problem.
Given a mark, determine its grade based on the table below:
74 < mark < 100 grade = A
64 < mark < 75 grade = B
54 < mark < 65 grade = C
39 < mark < 55 grade = D
0 < mark < 40 grade = E
others error message
TK1913-C Programming

31. A n s w e r 1 printf(“Key-in the mark: “); scanf(“%d”,&mark);
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”);
A n s w e r 1
TK1913-C Programming

32. A n s w e r 2 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 );
A n s w e r 2
TK1913-C Programming

33. A n s w e r 3 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);
A n s w e r 3
TK1913-C Programming

34. if statement that contains other if / if - else statements
Nested ifs
if statement that contains other if / if - else statements
TK1913-C Programming

35. Nested ifs Example: This price is valid for people: age > 55
if (age > 18) {
if (age > 55)
price = 2.50; /* Price for senior citizens */
else
price = 5.00; /* Price for adults */ }
else {
if (age < 1)
price = 0.0; /* Price for infants */
price = 1.50; /* for children & teenagers*/
This price is valid for people: age < 1
This price is valid for people: 1 < age < 18
TK1913-C Programming

36. Which if does this else belong to?
Nested ifs - Problem
Example:
if (age > 18)
if (age > 55)
price = 2.50; /* Price for senior citizens */
else
price = 5.00; /* Price for adults */
Which if does this else belong to?
TK1913-C Programming

37. Nested ifs - Problem Which one? 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; }
TK1913-C Programming

38. Nested ifs - Problem
By default, else will be attached to the nearest if
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;
TK1913-C Programming

39. switch and break switch (expression) { Don’t forget the brackets !!
The structure is similar to multiple selection (flowchart)
Syntax:
switch (expression) {
case expression1:
statement1;
break;
case espression2:
statement2; …
default:
expressionX; }
Syntax:
switch (expression) {
case expression1:
statement1;
break;
case espression2:
statement2; …
default:
expressionX; }
Don’t forget the brackets !!
Don’t forget the curly brackets !!
Don’t forget the colons !!
TK1913-C Programming

40. switch and break Must be INTEGER or CHAR ! Important Rule !! Syntax:
switch (expression) {
case expression1:
statement1;
break;
case espression2:
statement2; …
default:
expressionX; }
Must be INTEGER or CHAR !
TK1913-C Programming

41. switch and break Assume month = 1, so …
Example: switch (month) {
case 1:
printf(“January\n”);
break;
case 2:
printf(“February\n”);
case 3:
printf(“March\n”);
default:
printf(“Others\n”); }
printf(“End”);
Assume month = 1, so …
…this step will be executed. Later …
…case is terminated here. Jump to …
January
End _
January _
TK1913-C Programming

42. switch and break Assume month = 3, so …
Example: switch (month) {
case 1:
printf(“January\n”);
break;
case 2:
printf(“February\n”);
case 3:
printf(“March\n”);
default:
printf(“Others\n”); }
printf(“End”);
Assume month = 3, so …
March _
March
End _
…this step will be executed. Later …
…case is terminated here. Jump to …
TK1913-C Programming

43. Now…what will happen if this break is taken out from the program?
switch and break
Example: switch (month) {
case 1:
printf(“January\n”);
break;
case 2:
printf(“February\n”);
case 3:
printf(“March\n”);
default:
printf(“Others\n”); }
printf(“End”);
Example: switch (month) {
case 1:
printf(“January\n”);
break;
case 2:
printf(“February\n”);
case 3:
printf(“March\n”);
default:
printf(“Others\n”); }
printf(“End”);
Now…what will happen if this break is taken out from the program?
No more !!
TK1913-C Programming

44. switch and break Assume month = 2, so …
Example: switch (month) {
case 1:
printf(“January\n”);
break;
case 2:
printf(“February\n”);
case 3:
printf(“March\n”);
default:
printf(“Others\n”); }
printf(“End”);
February
March _
February
March
End _
February _
…this step will be executed. Later …
…execution continues. Thus, this step is executed . So …
…case is terminated here. Jump to …
TK1913-C Programming

45. Now…what will happen if these breaks are taken out from the program?
switch and break
Example: switch (month) {
case 1:
printf(“January\n”);
break;
case 2:
printf(“February\n”);
case 3:
printf(“March\n”);
default:
printf(“Others\n”); }
printf(“End”);
Now…what will happen if these breaks are taken out from the program?
And … if month = 34 ?
And … if month = 1 ?
TK1913-C Programming

46. Exercise To practice what you’ve learned, try exercises on page …
/* Do exercises from pg of Pengaturcaraan C
TK1913-C Programming

47. End of Lecture 7 (Part 2) At last, chap 7 is finished. What’s next???
Control Structure: Repetition on the way…
TK1913-C Programming