1. Lecture 2B Expressions Richard Gesick
Figures from Lewis, “C# Software Solutions”, Addison Wesley

2. Topics
Expressions
Data Conversion
Standard IO
Basic Libraries

3. Expression Combination of one or more operators and operands
Has both data type & value
Operands may be
literals
constants
variables

4. Arithmetic Operators Operator Operation + addition - subtraction *
multiplication /
division %
modulus (remainder after division between 2 integers)

5. Integer Division & Modulus
When dividing two integers:
the quotient is an integer
the remainder is truncated (discarded)
To get the remainder, use the modulus operator with the same operands

6. Examples 8
25 / 3
25 % 3
3 / 25
3 % 25
25.0 / 5
10 / 3.0 1 3
5.0

7. Operator Precedence Precedence Operator Associativity 1
Parenthesis: ()
Innermost First 2
Unary operators:
(type)
Right to left 3
Binary operators:
* / %
Left to right 4
+ - 5
Assignment Operators = += -= *= /= %=
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8. Operator Precedence
What is the order of evaluation in the following expressions?
a + b + c + d + e
a + b * c - d / e 1 2 3 4 3 1 4 2
a / (b + c) - d % e 2 1 4 3
a / (b * (c + (d - e))) 4 3 2 1

9. Assignment Revisited
The assignment operator has a lower precedence than the arithmetic operators
First the expression on the right hand
side of the = operator is evaluated
answer = sum / 4 + MAX * lowest; 4 1 3 2
Then the result is stored in the
variable on the left hand side

10. Assignment Revisited First the expression on the right hand
side of the = operator is evaluated
Expression has data type and value
variable = expression;
Then the result is stored in the
variable on the left hand side (has data type),
if types are compatible

11. Assignment Revisited
The right and left hand sides of an assignment statement can contain the same variable
First, one is added to the
original value of count
count = count + 1;
Then the result is stored back into count
(overwriting the original value)

12. Shortcut Operators ++ increment by 1 -- decrement by 1 Example:
count++; // count = count + 1;
count--; // count = count - 1;

13. Increment and Decrement
The increment and decrement operators can be applied in postfix form:
count++
or prefix form:
++count
When used as part of a larger expression, the two forms can have different effects
Because of their subtleties, the increment and decrement operators should be used with care

14. 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;

15. BUT...
when the increment (or decrement) operator is used in a statement with other operators, the prefix and postfix forms can yield different results
LET’S SEE HOW. . .

16. PREFIX FORM “First increment, then use ”
int alpha ; int num ; num = 13; alpha = ++num * 3; 13
num 14
alpha 42

17. POSTFIX FORM “Use, then increment ”
int alpha ; int num ; num = 13; alpha = num++ * 3; 13
num
alpha 13 39
num
alpha 14
num

18. More Shortcut Operators
Example
Equivalent +=
a += 3;
a = a + 3; -=
a -= 10;
a = a - 10; *=
a *= 4;
a = a * 4; /=
a /= 7;
a = a / 7; %=
a %= 10;
a = a % 10;

19. Assignment Operators is equivalent to
The right hand side of an assignment operator can be a complex expression
The entire right-hand expression is evaluated first, then the result is combined with the original variable
Therefore
result /= (total-MIN) % num;
is equivalent to
result = result / ((total-MIN) % num);

20. Common Error Trap
No spaces are allowed between the arithmetic operator and the equals sign
Note that the correct sequence is +=, not =+
Example: add 2 to a
// incorrect
a =+ 2; // a = +2; assigns 2 to 2
// correct
a += 2; // a = a + 2;

21. Topics
Expressions
Data Conversion

22. Assigning the Values of Other Variables
Syntax:
dataType variable2 = variable1;
Rules:
1. variable1 needs to be defined before this statement appears in the source code
2. variable1 and variable2 need to be compatible data types; in other words, the precision of variable1 must be lower than or equal to that of variable2.

23. Mixed-Type Arithmetic
When performing calculations with operands of different data types:
Lower-precision operands are promoted to higher-precision data types, then the operation is performed
Promotion is effective only for expression evaluation; not a permanent change
Called "implicit type casting"
Bottom line: any expression involving a floating-point operand will have a floating-point result.

24. Two types of data conversion
Widening conversion (promotion)
safe, do not lose data
goes to a “wider” (more bits) data type
may lose precision (long to float)
Narrowing conversion (demotion)
may lose data
may lose precision
should be avoided
compiler error unless specific cast done

25. Copyright © 2012 Pearson Education, Inc.
Order of Types
Because different types are different representations, frequently we need to convert between types.
Sometimes these conversions may lose information.
Conversion from lower types to higher types results in no loss of information.
Conversion from higher types to lower types may loose information.
High:
Low:
long double double float long integer integer short integer
Copyright © 2012 Pearson Education, Inc.

26. Conversion Techniques
assignment conversion
assign an int to a long
promotion
divide an int by a double
casting

27. Explicit Type Casting Syntax: (dataType)( expression )
Note: parentheses around expression are optional if expression consists of 1 variable
Useful for calculating averages
double result = (double) 25 / 3;
double result = (double) total / count;

28. Overflow and Underflow
answer too large to store
Example: using 16 bits for integers
result = ;
Exponent overflow
answer’s exponent is too large
Example: using float, with exponent range –38 to 38
result = 3.25e28 * 1.0e15;
Exponent underflow
answer’s exponent too small
result = 3.25e-28 *1.0e-15;
Copyright © 2012 Pearson Education, Inc.

29. Standard Input / Output
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30. C++ Input/Output No built-in I/O in C++
A library provides input stream and output stream
Keyboard
Screen
executing
program
istream
ostream 30

31. <iostream> Header File
Access to a library that defines 3 objects
An istream object named cin (keyboard)
An ostream object named cout (screen)
An ostream object named cerr (screen) 31

32. Giving a Value to a Variable
In your program you can assign (give) a value to the variable by using the assignment operator =
ageOfDog = 12;
or by another method, such as
cout << “How old is your dog?”;
cin >> ageOfDog;

33. >> Operator >> is called the input or extraction operator
>> is a binary operator
>> is left associative
Expression Has value
cin >> age cin
Statement
cin >> age >> weight;

34. Extraction Operator (>>)
Variable cin is predefined to denote an input stream from the standard input device((the keyboard)
The extraction operator >> called “get from” takes 2 operands; the left operand is a stream expression, such as cin--the right operand is a variable of simple type

35. Extraction Operator (>>)
Operator >> attempts to extract (inputs) the next item from the input stream and to store its value in the right operand variable
>> “skips over” (actually reads but does not store anywhere) leading white space characters as it reads your data from the input stream(either keyboard or disk file)

36. Input Statements SYNTAX These examples yield the same result.
cin >> length;
cin >> width;
cin >> length >> width;
cin >> Variable >> Variable . . .;

37. Whitespace Characters Include . . .
blanks
tabs
end-of-line (newline) characters
newline character created by:
hitting Enter or Return at the keyboard or
by using the manipulator endl or by using the symbols "\n" in the program

38. At keyboard you type: A[space]B[space]C[Enter]
char first;
char middle;
char last;
cin >> first ;
cin >> middle ;
cin >> last ;
NOTE: A file reading marker is left pointing to the newline character after the ‘C’ in the input stream
first
middle
last
‘A’
‘B’
‘C’
first
middle
last

39. At keyboard you type: [space]25[space]J[space]2[Enter]
int age;
char initial;
float bill;
cin >> age;
cin >> initial;
cin >> bill;
NOTE: A file reading marker is left pointing to the newline character after the 2 in the input stream
age
initial
bill 25
‘J’
2.0

40. Keyboard and Screen I/O
#include <iostream>
Keyboard
Screen
executing
program
input data
output data
cin
(of type istream)
cout
(of type ostream)

41. NOTE: shows the location of the file reading marker
STATEMENTS CONTENTS MARKER
POSITION
int i; A\n
char ch; \n
float x;
cin >> i; A\n
16.9\n
cin >> ch; A\n
cin >> x; A\n i ch x 25 i ch x 25
‘A’ i ch x 25
‘A’
16.9 i ch x

42. Another Way to Read char Data
The get() function can be used to read a single character.
get() obtains the very next character from the input stream without skipping any leading whitespace characters

43. At keyboard you type: A[space]B[space]C[Enter]
char first;
char middle;
char last;
cin.get(first);
cin.get(middle);
cin.get(last);
NOTE: The file reading marker is left pointing to the space after the ‘B’ in the input stream
first
middle
last
‘A’
‘ ’
‘B’
first
middle
last 43

44. Use function ignore() to skip characters
The ignore() function is used to skip (read and discard) characters in the input stream
The call:
cin.ignore(howMany, whatChar);
will skip over up to howMany characters or until whatChar has been read, whichever comes first

45. NOTE: shows the location of the file reading marker
STATEMENTS CONTENTS MARKER
POSITION
int a; \n
int b; \n
int c;
cin >> a >> b; \n \n
cin.ignore(100, ‘\n’); \n
cin >> c; \n a b c
957 34 a b c
957 34 a b c
957 34
128 a b c

46. Another Example Using cin.ignore()
NOTE: shows the location of the file reading marker
STATEMENTS CONTENTS MARKER
POSITION
int i; A 22 B 16 C 19\n
char ch;
cin >> ch; A 22 B 16 C 19\n
cin.ignore(100, ‘B’); A 22 B 16 C 19\n
cin >> i; A 22 B 16 C 19\n i ch
‘A’
957 34 i ch
‘A’
957 34 i ch 16
‘A’
957 34 i ch

47. String Input in C++
Input of a string is possible using the extraction operator >>
Example
string message;
cin >> message;
cout << message;
However . . .

48. >> Operator with Strings
Using the extraction operator(>>) to read input characters into a string variable
The >> operator skips any leading whitespace characters such as blanks and newlines
It then reads successive characters into the string
>> operator then stops at the first trailing whitespace character (which is not consumed, but remains waiting in the input stream)

49. String Input Using >>
string firstName;
string lastName;
cin >> firstName >> lastName;
Suppose input stream looks like this:
Joe Hernandez 23
What are the string values?

50. Results Using >>
string firstName;
string lastName;
cin >> firstName >> lastName;
Result
“Joe” “Hernandez”
firstName lastName

51. getline() Function
Because the extraction operator stops reading at the first trailing whitespace, >> cannot be used to input a string with blanks in it
Use the getline function with 2 arguments to overcome this obstacle
First argument is an input stream variable, and second argument is a string variable
Example
string message;
getline(cin, message);

52. getline(inFileStream, str)
getline does not skip leading whitespace characters such as blanks and newlines
getline reads successive characters(including blanks) into the string, and stops when it reaches the newline character ‘\n’
The newline is consumed by getline, but is not stored into the string variable

53. String Input Using getline
string firstName;
string lastName;
getline(cin, firstName);
getline(cin, lastName);
Suppose input stream looks like this:
Joe Hernandez 23
What are the string values?

54. Results Using getline string firstName; string lastName;
getline(cin, firstName);
getline(cin, lastName);
“ Joe Hernandez 23” ?
firstName lastName

55. Interactive I/O
In an interactive program the user enters information while the program is executing
Before the user enters data, a prompt should be provided to explain what type of information should be entered
The amount of information needed in the prompt depends on
the complexity of the data being entered, and
the sophistication of the person entering the data

56. Prompting for Interactive I/O
// Pattern: cout(prompt) cin(read value) cout << “Enter part number : “ << endl; cin >> partNumber; cout << “Enter quantity ordered : “ << endl; cin >> quantity; cout << “Enter unit price : “ << endl; cin >> unitPrice; // Calculate and print results

57. Prompting for Interactive I/O, cont...
totalPrice = quantity * unitPrice;
cout << “Part # “ << partNumber << endl;
cout << “Quantity: “ << quantity
<< endl;
cout << “Unit Cost: $ “ << setprecision(2)
<< unitPrice << endl;
cout << “Total Cost: $ “ << totalPrice

58. Manipulators and Methods
endl – places a newline character in the output buffer and flushes the buffer.
setf() and unsetf()
Flag
Meaning
ios::showpoint
display the decimal point
ios::fixed
fixed decimal notation
ios::scientific
scientific notation
Ios::setprecision(n)
set the number of significant digits to be printed to the integer value n
Ios::setw(n)
set the minimum number of columns for printing the
next value to the integer value n
ios::right
right justification
ios::left
left justification
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59. Building C++ Solutions with IDEs
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60. Integrated Development Environments (IDEs)
IDEs are software packages designed to facility the development of software solutions.
IDEs include:
Code editors
Compiler
Debugger
Testing tools
Many additional helpful tools…

61. Basic Functions in C++ Standard Library

62. Basic C++ Math Functions
fabs(x)
computes absolute value of x
sqrt(x)
computes square root of x, where x >=0
pow(x,y)
computes xy
ceil(x)
nearest integer larger than x
floor(x)
nearest integer smaller than x
exp(x)
computes ex
log(x)
computes ln x, where x >0
log10(x)
computes log10x, where x>0

63. Trigonometric Functions
sin(x)
sine of x, where x is in radians
cos(x)
cosine of x, where x is in radians
tan(x)
tangent of x, where x is in radians
asin(x)
This function computes the arcsine, or inverse sine, of x, where x must be in the range [−1, 1].
The function returns an angle in radians in the range [−π/2, π/2].
acos(x)
This function computes the arccosine, or inverse cosine, of x, where x must be in the range [−1, 1].
The function returns an angle in radians in the range [0, π].
atan(x)
This function computes the arctangent, or inverse tangent, of x.
atan2(y,x)
This function computes the arctangent or inverse tangent of the value y/x.
The function returns an angle in radians in the range [−π, π].

64. Common Functions Defined in <cctype>
isalpha(ch)
Returns true if ch is an upper or lower case letter.
isdigit(ch)
Returns true if ch is a decimal digit
isspace(ch)
Returns true if ch is a whitespace character.
islower(ch)
Returns true if ch is an lower case letter.
isupper(ch)
Returns true if ch is an upper case letter.
tolower(ch)
Returns the lowercase version of ch if ch is an uppercase character, returns ch otherwise.
toupper(ch)
Returns the uppercase version of ch if ch is a lowercase character, returns ch otherwise.

65. Copyright © 2012 Pearson Education, Inc.
System Limitations
C++ standards do not specify limitations of data types – they are compiler-specific.
C++ does provide standard methods of accessing the limits of the compiler:
<climits> defines ranges of integer types.
<cfloat> defines ranges of floating-point types.
the sizeof(type) function returns the memory size of the type, in bytes.
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66. Summary
What did you learn?