1. Lecture no 3
Control statements

2. Selection in C++
If statements

3. Selection If or if / else statement
choosing between mutually exclusive possibilities
Two forms
if (logical expression) statement;
else statement;

4. Logical Expressions relational operators binary operators
==, !=, <=, >=, >, <
binary operators
work on any type of data, be careful about matching types
watch out for = and ==
produce a bool result

5. Syntax of if statement if (logical expression) statement;
don't put semicolon after condition
indentation helps humans, doesn't matter to compiler
can't start statement with "else"

6. Syntax of if statement if (x > 0) y = sqrt(x); if (x > y)
t = x; x = y; y = t; // what goes with the if?

7. If-Then Statement TRUE expression FALSE statement
Determine whether or not to execute a statement (which can be a single statement or an entire block)
TRUE
expression
FALSE
statement

8. Examples output larger of two numbers
don't allow sqrt of negative number
don't allow overflow
determining even or odd
give student another chance at a question

9. Visual Aid
Decision tree

10. Example What is output? Why? int age; age = 20; if (age = 16) {
cout << “Did you get driver’s license?”; }

11. Example What is output? Why? int age; age = 30; if (age < 18)
cout << “Do you drive?”;
cout << “Too young to vote”;

12. Example What is output? Why? int number; number = 0; if (number = 0)
cout << “Zero value”;
else
cout << “Non-zero value”;

13. Logical Operators And && Or || Not ! binary operators
used to combine bool values
produce a bool result
truth tables
operator precedence
! then && then ||

14. Logical
Expression Meaning Description
! p NOT p ! p is false if p is true
! p is true if p is false
p && q p AND q p && q is true if
both p and q are true.
It is false otherwise.
p || q p OR q p || q is true if either
p or q or both are true It is false otherwise.

15. Converting English to logic
"0 is less than x is less than 5"
"x is 5 or 6"
"x is bigger than 5 and less than 10"
impossible situations "dead code"
always true
always false

16. Write an expression for each
taxRate is over 25% and income is less than $20000
temperature is less than or equal to 75 or humidity is less than 70%
age is over 21 and age is less than 60
age is 21 or 22

17. Some Answers (taxRate > .25) && (income < 20000)
(temperature <= 75) || (humidity < .70)
(age > 21) && (age < 60)
(age == 21) || (age == 22)

18. What went wrong?
This is only supposed to display “HEALTHY AIR” if the air quality index is between 50 and 80.
But when you tested it, it displayed “HEALTHY AIR” when the index was 35.
int AQIndex;
AQIndex = 35;
if (50 < AQIndex < 80)
cout << “HEALTHY AIR“;

19. Analysis of Situation AQIndex = 35;
According to the precedence chart, the expression
(50 < AQIndex < 80) means
(50 < AQIndex) < because < is Left Associative
(50 < AQIndex) is false (has value 0)
(0 < 80) is true.

20. Corrected Version int AQIndex; AQIndex = 35;
if ((50 < AQIndex) && (AQIndex < 80))
cout << “HEALTHY AIR“;

21. Nested if's
the statement to be executed in an if statement can be another if

22. Example 100.0 average = 100.0; if (average >= 60.0)
float average;
average = 100.0;
if (average >= 60.0)
if (average < 70.0)
cout << “Marginal PASS”;
else
cout << “FAIL”;
FAIL is printed; WHY? The compiler ignores indentation and pairs the else with the second if
100.0
average

23. Example
Quadrant determination

24. if .. else provides two-way selection
between executing one of 2 clauses (the if clause or the else clause)
TRUE
FALSE
expression
if clause
else clause

25. What happens if you omit braces?
if ((carDoors == 4) && (driverAge > 24))
premium = ;
cout << “ LOW RISK “;
else
premium = ;
cout << “ HIGH RISK ”;
monthlyPayment = premium / ;
Compile error occurs: The “if clause” is the single statement following the if

26. Another form of nested if's
if (condition)
statement;
else if (condition)
else

27. Comparing Strings
Two objects of type string (or a string object and a C string) can be compared using the relational operators
A character-by-character comparison is made using the ASCII character set values
If all the characters are equal, then the 2 strings are equal. Otherwise, the string with the character with smaller ASCII value is the “lesser” string

28. myState > yourState true
string myState;
string yourState;
myState = “Texas”;
yourState = “Maryland”;
Expression Value
myState == yourState false
myState > yourState true
myState == “Texas” true

29. Test Plan if (x + y > 0) cout << "safe"; else if (x > 3)
cout << "high";
else cout << "low";

30. Test Plan Case Input Output (expected) Output (actual) x + y > 0
"safe"
x + y <=0, x > 3
x = 5, y=-7
"high"
x+y <=0, x <= 3
x = 2, y=-3
"low"

31. Operator Meaning Associativity
! NOT Right
*, / , % Multiplication, Division, Modulus Left
+ , - Addition, Subtraction Left
< Less than Left
<= Less than or equal to Left
> Greater than Left
>= Greater than or equal to Left
== Is equal to Left
!= Is not equal to Left
&& AND Left
|| OR Left
= Assignment Right 31

32. Comparing Real Values
Do not compare floating point values for equality, compare them for near-equality.
float myNumber;
float yourNumber;
cin >> myNumber;
cin >> yourNumber;
if (fabs (myNumber - yourNumber) < )
cout << “They are close enough!” << endl;

33. Lecture 3-b

34. Data Types, Expressions and Functions (part I)

35. Topics constants of type int and float
evaluating arithmetic expressions
implicit type coercion and explicit type conversion
calling a value-returning function
using function arguments
using C++ library functions in expressions

36. Standard Data Types in C++
Integral Types
represent whole numbers and their negatives
declared as int, short, or long
Floating Types
represent real numbers with a decimal point
declared as float or double
Character Type
represents single characters
declared as char

37. Samples of C++ Data Values
int sample values
float sample values
9521E E E2
char sample values
‘B’ ‘d’ ‘4’ ‘?’ ‘*’

38. Scientific Notation 2.7E-4 means 2.7 x 10 - 4 = 2.7000 = 27000.0=
2.7E-4 means x = =

39. More About Floating Point Values
Floating point numbers have an integer part and a fractional part, with a decimal point in between. Either the integer part or the fractional part, but not both, may be missing
Examples
Alternatively, floating point values can have an exponent, as in scientific notation--the number preceding the letter E doesn’t need to include a decimal point (E can be upper or lower case)
Examples E E E E3

40. Division Operator
The result of the division operator depends on the type of its operands
If one or both operands has a floating point type, the result is a floating point type. Otherwise, the result is an integer type (truncates!!)
Examples / has value / has value / has value
11.0 / 4 has value

41. Find the Middle //***************************************************
// FreezeBoil program
// This program computes the midpoint between
// the freezing and boiling points of water
#include < iostream >
using namespace std;
const float FREEZE_PT = 32.0; // Freezing point of water
const float BOIL_PT = ; // Boiling point of water
int main() {
float avgTemp; // Holds the result of averaging
// FREEZE_PT and BOIL_PT

42. Find the Middle (continued)
cout << “Water freezes at “ << FREEZE_PT << endl;
cout << “ and boils at “ << BOIL_PT
<< “ degrees.” << endl;
avgTemp = FREEZE_PT + BOIL_PT;
avgTemp = avgTemp / 2.0;
cout << “Halfway between is “;
cout << avgTemp << “ degrees.” << endl;
return 0; }

43. Modulus Operator
The modulus operator % can only be used with integer type operands and always has an integer type result
Its result is the integer type remainder of an integer division
Example % 4 has value 3 because
R = ? ) 4 11

44. More C++ Operators
RAM
int age;
age = 8;
age = age + 1;
age 8 9

45. Prefix Form Increment Operator
int age;
age = 8;
++age; 8
age 9
age

46. Postfix Form Increment Operator
int age;
age = 8;
age++; 8
age 9
age

47. Decrement Operator
int dogs;
dogs = 100;
dogs--;
100
dogs 99
dogs

48. Which Form to Use
When the increment(or decrement) operator is used in a “stand alone” statement solely to add one(or subtract one) from a variable’s value, it can be used in either prefix or postfix form
USE EITHER
dogs--; dogs;

49. BUT...
You can use increment or decrement operators INSIDE other statements
example: y = ++x;
example: if ( x ++ > 0) cout << x;
You can write very confusing statements!
example: x = x x; // compiles!
This is NOT a good idea!!!!
Use ++ and -- in stand alone statements only!

50. What is an Expression in C++?
An expression is a valid arrangement of variables, constants, and operators
In C++ each expression is evaluated to a value of a given type
The value of the expression 9.3 * 4.5 is
The type of the expression 9.3 * 4.5 is float

51. Operators can be binary involving 2 operands 2 + 3
unary involving 1 operand
ternary involving 3 operands don't!

52. Some of the C++ Operators
Precedence Operator Description
Higher ( ) Function call
+ Positive (unary)
- Negative (unary)
* Multiplication
/ Division
% Modulus(remainder)
+ Addition (binary)
- Subtraction (binary
Lower = Assignment

53. Precedence
Precedence determines which operator is applied first in an expression having several operators
higher precedence operators are done first

54. Associativity
Left to right associativity means that in an expression having 2 operators with the same priority, the left operator is applied first
In C++ the binary operators
*, /, %, +, - are all left associative
Expression means (9 - 5) - 1
4 - 1 3

55. Evaluate the Expression
7 * % 3 *
(7 * 10) % 3 *
% 3 *
70 -(5 % 3) * *
70 - ( 2 * 4) + 9
( ) 71

56. Parentheses Parentheses can be used to change the usual order
Parts in() are evaluated first
Evaluate (7 *(10 - 5) % 3) *
(7 * 5 % 3 ) *
( 35 % 3) *
2 * 17

57. Assignment Operator semantics
Variable = Expression
First the expression on right is evaluated
Then the resulting value is stored in the memory location of variable on left
NOTE: An automatic implicit type coercion occurs after evaluation but before the value is stored if the types differ for expression and variable

58. What value is stored? float a; float b; a = 8.5; b = 9.37; a = b; 8.5

59. What is stored? float someFloat; ?
someFloat = 12; // Causes implicit type conversion ?
12.0
someFloat

60. What is stored? int someInt; ?
someInt = 4.8; // Causes implicit type conversion ? 4
someInt

61. Type Casting is Explicit Conversion of one Type to another
int(4.8) has value 4
float(5) has value 5.0
float(7/4) has value 1.0
float(7) / float(4) has value 1.75

62. Some Expressions age = 8 8 - age - 8 5 + 8 13 5 / 8 0 6.0 / 5.0 1.2
int age;
Example Value
age =
- age
5 /
6.0 /
float(4 / 8)
float(4) /

63. What values are stored? float loCost; float hiCost; loCost = 12.342;
float(int(loCost * )) / 100.0;
hiCost =
float(int(hiCost * )) / 100.0;

64. Values were rounded to 2 decimal places
loCost
12.34
12.35
hiCost

65. Functions Recall every C++ program must have a function called main
Program execution always begins with function main
Any other functions are subprograms and must be called

66. Function Calls
One function calls another by using the name of the called function together with() containing an argument list
x = sqrt (25.0);
A function call temporarily transfers control from the calling function to the called function (that's why it's a control structure)

67. Value-Returning Functions HEADER FILE FUNCTION EXAMPLE VALUE OF CALL
<cstdlib> abs(i) abs(-6)
<cmath> pow(x,y) pow(2.0,3.0)
fabs(x) fabs(-6.4)
<cmath> sqrt(x) sqrt(100.0)
sqrt(x) sqrt(2.0)
<cmath> log(x) log(2.0)
<cctype> isupper(c) isupper('A') true

68. Write C++ Expressions for
The square root of b2 - 4ac
sqrt(b * b * a * c)
The square root of the average of myAge and yourAge
sqrt((myAge + yourAge) / 2)

69. Function Call
A function call temporarily transfers control to the called function’s code
When the function’s code has finished executing, control is transferred back to the calling block

70. Function Call Syntax FunctionName ( Argument List )
The argument list is a way for functions to communicate with each other by passing information
The argument list can contain zero, one, or more arguments, separated by commas, depending on the function