1. Chapter 4 (Conditional Statements)
Problem Solving and Program Design in C (5th Edition) by Jeri R. Hanly and Elliot B. Koffman
Chapter 4
(Conditional Statements)
© CPCS 202
1431/1432 – Term 1

2. CHAPTER 4 - Conditional Statements#
CHAPTER 4 - Conditional Statements
Simple Logic Expression
Complex Logic Expression
Evaluation Tree
Conditional Statements
IF Statement
Switch Statement
Common Errors in Conditions
ATM Simulation 1
ATM Simulation 2
 column shows the topics index.  column shows the programs index.

3. Simple Logic Expression1
Simple Logic Expression
Introduction
often need to look at data values and make choices
logical expressions are true/false statements of data relationships
Prototype
variables or constants
relational or equality
variables or constants
data operator data
Simple Logic Expression
Operator
Less than
<
Larger than
>
Less than or equal
<=
Simple Logic Expression
Operator
Larger than or equal
>=
Equal ==
Not equal !=

4. Simple Logic Expression1
Simple Logic Expression
Example
let a = 17 and b = 42
(a < b) True
(a > b) False
(a <= b) True
(a >= b) False
(a == b) False
(a != b) True
Statement has ! may confuse you, so read it without ! and flip the result

5. Complex Logic Expression2
Complex Logic Expression
Introduction
combining more than one simple logic expressions make it a complex logical expression
Prototype
expression operator expression
AND && OR || NOT !
Logic Expression
Result
TRUE && TRUE
TRUE
TRUE && FALSE
FALSE
FALSE && TRUE
FALSE && FALSE
Logic Expression
Result
TRUE || TRUE
TRUE
TRUE || FALSE
FALSE || TRUE
FALSE || FALSE
FALSE
Logic Expression
Result
! TRUE
FALSE
! FALSE
TRUE
Imagine 1 light with 2 switches; the operator between them is &&, ||, or !

6. Complex Logic Expression2
Complex Logic Expression
Example
let x = 3.14 and y = 7.89
((x < 4)&&(y < 8)) True (both halves are true)
((x > 3)&&(y > 8)) False (second half is false)
((x < 4)||(y > 8)) True (first half is true)
((x < 3)||(y < 8)) True (second half is true)
((x > 4)||(y > 8)) False (both halves are false)
!(x < y) False
!(x >= y)  True
!(a == b) True
!(a != b) False

7. Evaluation Tree (Step-by-Step)3
Evaluation Tree (Step-by-Step)
Introduction
a way to solve a logic expression
Way to Do
solve the simple logic expression first
Example
((x < 5)&& !(y > 9)) (x=4 ; y=5) T
<
> F T !
&& T

8. Evaluation Tree (Step-by-Step)3
Evaluation Tree (Step-by-Step)
Introduction
a way to solve a logic expression
Way to Do
solve the simple logic expression first
Example
((x < 5)&& !(y > 9)) (x=4 ; y=5)
TRUE T T F
SECOND
way

9. Conditional Statements4
Conditional Statements
Overview
control the flow of your program
based on True or False
allow selecting an action based on condition
two types of the conditional statements available in C:
if statements
Switch statements

10. Conditional Statements – IF Statements
Overview
three types of the IF statements:
IF (allows the flow of the program to be changed if the IF statement condition is True)
IF-ELSE (gives an alternative path to be executed if the IF statement condition is False)
Nested IF (IF statements insides IF statements)

11. Conditional Statements – IF Statements (IF)
Introduction
can selectively execute code using if statement
when logical expression is true, selected code is executed
when logical expression is false, selected code is skipped
selected code can be either a single statement or a block of statements which is enclosed in { } characters
should indent code to aid program readability
no need for semi-colon after IF statements 1 2 3
Condition 5 6 7 4 T

12. Conditional Statements – IF Statements (IF)
Prototype
If you have only one statement after an if statement, you do not need to (but you can) put the statement in braces. For example:
To have more than one statement execute after an if statement that evaluates to true, use braces. For example: 1 2
Condition T 3 2. 3. 4.
if ( TRUE ) Statement executes if condition is True Statement executes if condition is True/False 4 1 2
Condition T 2. 3. 4. 5. 6.
if ( TRUE ) {    
All the statements in this block execute if the condition is True } 3 4 5
Statements between braces are called a compound statement, or a block

13. Conditional Statements – IF Statements (IF)
Example
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scanf(“%d”, &a); scanf(“%d”, &b); if (b > a)    printf ("B is larger than A\n“); printf (“Done...\n“); 3 T 4 5 1. 2. 3. 4. 5. 6. 7. 8.
scanf(“%d”, &a); scanf(“%d”, &b); if (a < b) {    printf("A is smaller than B\n“);    printf("The difference is %d\n“, b–a); } printf (“Done...\n“);
1-2 3 T
5-6 8
In a diagram, you can merge the sequential statements in one block

14. Conditional Statements – IF Statements (IF-ELSE)
Introduction
often need two alternatives in an IF statement
want to execute certain code if expression is true
want to execute different code if expression is false
the if-else statement lets you do this
can use single statement or block of code for either part
should indent code to aid program readability 1 2 3
Condition F T 4 5 6 7 8

15. Conditional Statements – IF Statements (IF-ELSE)
Prototype
if ( condition 1 ) {    // A. Execute these statements // if condition 1 is TRUE } else if ( condition 2 ) {    // B. Execute these statements // if condition 2 is TRUE }
else if ( condition 3 ) {    // C. Execute these statements // if condition 3 is TRUE }
else {    // D. Execute these statements // if condition 1, 2 and 3 are FALSE }
Cond.1 F A T
Cond.2 F
Cond.3 B T F D C T
The same
The compiler looks at the entire program in one line unless there is ;

16. Conditional Statements – IF Statements (IF-ELSE)
Example 1. 2. 3. 4. 5. 6. 7. 8. 9.
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printf(“Enter the grade for the course: ”); scanf(“%d”, &grade); if (grade >= 90) printf(“GPA = A\n”); else if (grade >= 80) printf(“GPA = B\n”); else if (grade >= 70) printf(“GPA = C\n”); else if (grade >= 60) printf(“GPA = D\n”); else { printf(“GPA = F\n”); printf(“UNSATISFACTORY.\n”); }
Quiz: draw the flow diagram for this segment?

17. Conditional Statements – IF Statements (Nested IF)
Introduction
often need to check one condition within another
can nest if statements to accomplish this
need to take care when matching up { } brackets
use indentation to reflect nesting and aid readability

18. Conditional Statements – IF Statements (Nested IF)
Prototype if (expression 1)
{    // A. statements    if (expression 2)
{       // B. statements    }    else
  {       // C. statements       if (expression 3)
  {          // D. statements       }    } } else {    // E. statements    if (expression 4)   {       // F. statements    } }
Exp. 1 T F E
Exp. 4 F T A
Exp. 2 T F C
Exp. 3 D T B

19. Conditional Statements – IF Statements (Nested IF)
How many PATHs you have?
1, 3, 5, 8
1, 3, 5, 7, 9, 10
1, 3, 5, 7, 9
1, 2, 4, 6
1, 2, 4 1 F T 2 3 4 5 T F T 7 8 6 9 T 10

20. Conditional Statements – IF Statements (Nested IF)
Example 1. 2. 3. 4. 5. 6. 7. 8. 9.
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if (a > 0) {    if (b < 0) {     a = 3 * b;    c = a + b; } } else {    a = 2 * a;    c = b / a; }
Quiz: draw the flow diagram for this segment?

21. Conditional Statements – IF Statement
Conclusion 1 1 1 2 2 2 3
Condition
Condition T F T 3 4 3 4 5 4 5 6 5 6 7 6 7
Sequential IF
IF / ELSE
In a diagram, you can merge the sequential blocks in one block

22. P1
ATM Simulation 1
Write a program that simulates an ATM, where they are three main options:
Deposit Money
Withdraw Money
Print Balance
Assume the balance in the account is Zero
Use if to choose an option from the Main Menu

23. ATM Simulation 1 P1 Input Output Formula An option from the main menu
Amount of money to deposit if the user choose option 1
Amount of money to withdraw if the user choose option 2
Output
The balance if the user choose option 3
Formula
Balance = Balance + Deposit if the user choose option 1
Balance = Balance – Withdraw if the user choose option 2
Think about the input/formula/output for each option in the main menu

24. ATM Simulation 1 P1 Initial the balance balance = 0
Ask the user to choose one of the 3 options  command
Deposit Money
Get the amount of money that wants to deposit  money
Calculate the balance
balance = balance + money
Withdraw Money
balance = balance - money
Display the balance  balance 1 2 3

25. P1
ATM Simulation 1 1. 2. 3. 4. 5. 6. 7. 8. 9.
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#include <stdio.h>
int main(void) {
int command; // Input: an option from the main menu
int money; // Input: withdraw or deposite money
int balance; // Output: Display the balance
/* 1. Initial the balance */
/* 2. Ask the user to choose one of the 3 options */
if (command == 1) /* 2.1 Deposit Money */ }
else if (command == 2) /* 2.2 Withdraw Money */
else if (command == 3) /* 2.3 Print Balance */
return(0);

26. ATM Simulation 1 P1 1. #include <stdio.h> 2. 3. int main(void){
int command; // Input: an option from the main menu
int money; // Input: withdraw or deposite money
int balance; // Output: Display the balance
/* 1. Initial the balance */
balance = 0;
/* 2. Ask the user to choose one of the 3 options */
printf(" Main Menu\n");
printf(" \n");
printf(" 1 - Deposit money\n");
printf(" 2 - Withdraw money\n");
printf(" 3 - Print balance\n");
printf("Enter command number: ");
scanf("%d", &command);
if (command == 1) /* 2.1 Deposit Money */
printf("Enter deposit amount: ");
scanf("%d", &money);
balance = balance + money; }
else if (command == 2) /* 2.2 Withdraw Money */
printf("Enter withdraw amount: ");
balance = balance - money;
else if (command == 3) /* 2.3 Print Balance */
printf("Current balance = %d\n", balance);
return(0); 1. 2. 3. 4. 5. 6. 7. 8. 9.
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27. P1
ATM Simulation 1
Useless program because it doesn’t have a loop to see the new balance

28. P1
ATM Simulation 1
Validation Check: If a user put an invalid input, you need to display an error message
Maintain the program to validate the inputs? input has to be 1,2,3 only

29. ATM Simulation 1 P1 #include <stdio.h> int main(void) {
int command; // Input: an option from the main menu
int money; // Input: withdraw or deposite money
int balance; // Output: Display the balance
/* 1. Initial the balance */
balance = 0;
/* 2. Ask the user to choose one of the 3 options */
printf(" Main Menu\n");
printf(" \n");
printf(" 1 - Deposit money\n");
printf(" 2 - Withdraw money\n");
printf(" 3 - Print balance\n");
printf("Enter command number: ");
scanf("%d", &command);
if (command == 1) /* 2.1 Deposit Money */
printf("Enter deposit amount: ");
scanf("%d", &money);
balance = balance + money; }
else if (command == 2) /* 2.2 Withdraw Money */
printf("Enter withdraw amount: ");
balance = balance - money;
else if (command == 3) /* 2.3 Print Balance */
printf("Current balance = %d\n", balance);
else /* Otherwise, display an error */
printf("Error choice...\n");
return(0); 1. 2. 3. 4. 5. 6. 7. 8. 9.
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30. P1
ATM Simulation 1

31. Conditional Statements – Switch Statement4b
Conditional Statements – Switch Statement
Introduction
switch statement convenient for handling multiple if-else cases
need to use single value as decision variable (called: controlling expression) of type: int or char, but not of type double
need to identify code to be executed for each case
it is essential to end each case with break command
can use default for all cases not specifically labeled
Prototype
switch ( decision value ) {    case label1 : statements;       break;    case label2: statements;       break;    default: statements; }

32. Conditional Statements - Switch Statement4b
Conditional Statements - Switch Statement
Examples
switch (command) {
case 1:
printf(“Light is ON.\n");
break;
case 2: printf(“Light is OFF.\n");
  default:   printf("Error Option!\n"); } 1. 2. 3. 4. 5. 6. 7. 8. 9.
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11. 3 4 T F 6 7 10
switch (command) {
case 1:
printf(“Light is ON.\n");
break;
case 2: printf(“Light is OFF.\n");
  default:   printf("Error Option!\n"); } 1. 2. 3. 4. 5. 6. 7. 8. 9.
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switch (command) {
case 1:
printf(“Light is ON.\n");
break;
case 2: printf(“Light is OFF.\n");
  default:   printf("Error Option!\n"); } 1. 2. 3. 4. 5. 6. 7. 8. 9.
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33. P2
ATM Simulation 2
Write a program that simulates an ATM, where they are three main options:
Deposit Money
Withdraw Money
Print Balance
Assume the balance in the account is Zero
Use if to choose an option from the Main Menu
Validate the input; if a user choose a wrong option, display an error message
As same as Program 1, but use Switch statement instead of IF

34. ATM Simulation 2 P2 Input Output Formula An option from the main menu
Amount of money to deposit if the user choose option 1
Amount of money to withdraw if the user choose option 2
Output
The balance if the user choose option 3
An error message if the user choose a wrong option
Formula
Balance = Balance + Deposit if the user choose option 1
Balance = Balance – Withdraw if the user choose option 2
Think about the input/formula/output for each option in the main menu

35. ATM Simulation 2 P2 Initial the balance balance = 0
Ask the user to choose one of the 3 options  command
Deposit Money
Get the amount of money that wants to deposit  money
Calculate the balance
balance = balance + money
Withdraw Money
balance = balance - money
Print Balance
Display the balance  balance
Display an error message 1 2 3
Error Option

36. P2
ATM Simulation 2 1. 2. 3. 4. 5. 6. 7. 8. 9.
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#include <stdio.h>
int main(void) {
int command; // Input: an option from the main menu
int money; // Input: withdraw or deposite money
int balance; // Output: Display the balance
/* 1. Initial the balance */
/* 2. Ask the user to choose one of the 3 options */
switch (command)
case 1: /* 2.1 Deposit Money */
break;
case 2: /* 2.2 Withdraw Money */
case 3: /* 2.3 Print Balance */
default: /* Otherwise, Error Message */ }
return(0);

37. ATM Simulation 2 P2 #include <stdio.h> int main(void) {
int command; // Input: an option from the main menu
int money; // Input: withdraw or deposite money
int balance; // Output: Display the balance
/* 1. Initial the balance */
balance = 0;
/* 2. Ask the user to choose one of the 3 options */
printf(" Main Menu\n");
printf(" \n");
printf(" 1 - Deposit money\n");
printf(" 2 - Withdraw money\n");
printf(" 3 - Print balance\n");
printf("Enter command number: ");
scanf("%d", &command);
switch (command)
case 1: /* 2.1 Deposit Money */
printf("Enter deposit amount: ");
scanf("%d", &money);
balance = balance + money;
break;
case 2: /* 2.2 Withdraw Money */
printf("Enter withdraw amount: ");
balance = balance - money;
case 3: /* 2.3 Print Balance */
printf("Current balance = %d\n", balance);
default: /* Otherwise, Error Message */
printf("Error choice...\n"); }
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38. P2
ATM Simulation 2

39. Common Errors in Conditions5
Common Errors in Conditions
if (0 <= x <= 4) printf(“Condition is true.\n”);
if (x = 10) printf(“x is 10.\n”);
if (x > 0) sum = sum + x; printf(“Greater than zero.\n”); else printf(“Less than or equal to zero”);
Make sure to indent the block of statements to clear the readability

40. Evaluation Homework hw
The 2nd example in IF-ELSE described transferring the number grades to letter grades. Write a program for this problem using a Switch statement without any IF statement?
The result of the following logic expression is: flag && !(y + z >= x – z) where (flag=0; x=3; y=4; z=2)
True
False
The output of the following flow diagram if (X=1) is: 1 2 3 13 23
X>2
printf(“2”);
printf(“1”);
printf(“3”); T F

41. Evaluation Homework hw
Type Program 2 and display the result when case = 2 (Print a copy of the code and a snapshot of the output) , and then remove the break from the second case. (Display the output only in the same page when case=2) Describe what happened when break was removed? (put the answer at the end of the same page)
Re-write the following program them after fixing the errors? Show the output and draw the flow diagram? 1. 2. 3. 4. 5. 6. 7. 8. 9.
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double fee(int speed) {
IF (speed > 160)
money = ;
elseif (speed > 140)
money = ;
Else
money = ;
  return (money); }
int main(void) {
  printf(“What is the speed of the car:”); scanf(“%d”, &speed);
printf(“Speed = %d, Ticket = %f\n”, speed, fee(speed));

42. CHAPTER 4 - Conditional Statements#
CHAPTER 4 - Conditional Statements
Simple Logic Expression
Complex Logic Expression
Evaluation Tree
Conditional Statements
IF Statement
Switch Statement
Common Errors in Conditions
ATM Simulation 1
ATM Simulation 2
 column shows the topics index.  column shows the programs index.