1. Variables and Special Chars (Ch. 2, 3)
Basic C++ Programming
Review
Variables
and
Special Chars
(Ch. 2, 3)
COMP103 - C++ Review

2. Valid Variable Names Rules for variable names in C++ (page 33)
The first character must be an alphabetic character or underscore
Consists only of alpha-numeric and underscore characters
Cannot duplicate a reserved word (see Appendix B)
Valid Names
a PI
student_name _PI
_assign1
Invalid Names
$a for
2name a a
int
COMP103 - C++ Review

3. Important Special Characters
As a Character In a String
Return \n
Null
Single Quote
Double Quote
Backslash
‘\n’
‘\0’
‘\’’
‘\”’
‘\\’
“\n” “”
“’”
“\””
“\\”
Backslash (\) indicates special character follows.
COMP103 - C++ Review

4. Constant declarations
Constants are used to store values that never change during the program execution.
Using constants makes programs more readable and maintainable.
Syntax:
const <type> <identifier> = <expression>;
Examples:
const double US2HK = 7.8;
//Exchange rate of US$ to HK$
const double HK2TW = 3.98;
//Exchange rate of HK$ to TW$
const double US2TW = US2HK * HK2TW;
//Exchange rate of US$ to TW$
COMP103 - C++ Review

5. Variable declarations
Variables are used to store values that can be changed during the program execution.
A variable is best thought of as a container for a particular type of data/value.
You must specify the variables type when you declare it
Syntax:
< type > < identifier >;
< type > < identifier > = < expression >;
Examples:
int sum;
int i = j = 0;
int total = 3445;
char answer = 'y';
double temperature = -3.14;
COMP103 - C++ Review

6. Variable declarations
Variables are not automatically initialized. For example, after declaration
int sum;
the value of the variable sum can be anything (garbage).
Thus, it is good practice to initialize variables when they are declared.
A variable has a type and it can contain only values of that type. For example, a variable of the type int can only hold integer values.
Once a value has been placed in a variable it stays there until the program deliberately alters it.
Demonstrate the last point by example: IF-1.cpp in subdir Examples-on-Decision-Ch5
COMP103 - C++ Review

7. Character data
A variable or a constant of char type can hold an ASCII character (see Appendix A of the textbook).
When initializing a constant or a variable of char type, or when changing the value of a variable of char type, the value is enclosed in single quotation marks.
Examples:
const char star = '*';
char letter, one = '1';
COMP103 - C++ Review

8. Programming
Decisions
(Ch. 5)
COMP103 - C++ Review

9. The Basic if Statement Syntax if(Expression)
Action
If the Expression is true then execute Action
Action is either a single statement or a group of statements within braces
Expression
Action
true
false
COMP103 - C++ Review

10. Choice (if) Example: find the absolute value
if (value < 0)
value = -value;
Can put multiple action statements within braces
if <it's raining> {
<take umbrella>
<wear raincoat> }
COMP103 - C++ Review

11. Sorting Two Numbers int value1; int value2; int temp;
cout << "Enter two integers: ";
cin >> value1 >> value2;
if(value1 > value2){
temp = value1;
value1 = value2;
value2 = temp; }
cout << "The input in sorted order: "
<< value1 << " " << value2 << endl;
Example: If-1.cpp
COMP103 - C++ Review

12. Relational Operators
Relational operators are used to compare two values
Math C++ Plain English
= == equals [example: if(a==b) ]
BUT (a=b) means put the value of b into a
< < less than
 <= less than or equal to
> > greater than
 >= greater than or equal to
 != not equal to
Example: If-Else-Tricky.cpp Correct syntax of “equal” is “==“
COMP103 - C++ Review

13. A Boolean Type
C++ contains a type named bool which can have one of two values
true (corresponds to non-zero value)
false (corresponds to zero value)
Boolean operators can be used to form more complex conditional expressions
The AND operator is &&
The OR operator is ||
The NOT operator is !
Warning
& and | are bitmap operators
COMP103 - C++ Review

14. More Operator Precedence
Precedence of operators (from highest to lowest)
Parentheses ( … )
Unary operators !
Multiplicative operators * / %
Additive operators + -
Relational ordering < <= >= >
Relational equality == !=
Logical and &&
Logical or ||
Assignment =
COMP103 - C++ Review

15. Examples of bool Assignments to bool type variables
bool P = true; bool Q = false; bool R = true; bool S = P && Q; // F bool T = !Q || R; // T bool U = !(R && !Q); // F
COMP103 - C++ Review

16. Operator Precedence: Examples
5 != 6 || 7 <= 3
is equivalent to
(5 !=6) || (7 <= 3)
5 * == 13 && 12 < 19 || !false == 5 < 24
is TRUE
Example: Boolean.cpp
COMP103 - C++ Review

17. The if-else Statement Syntax if (Expression) Action1 else Action2
 If Expression is true
then execute Action1
otherwise execute Action2
Expression
Action1
Action2
true
false
COMP103 - C++ Review

18. The if-else Statement if <it's sunny>{
<go to beach with sun block> }
else{
<take umbrella>
COMP103 - C++ Review

19. Finding the Big One int value1; int value2; int larger;
cout << "Enter two integers: ";
cin >> value1 >> value2;
if (value1 > value2)
larger = value1;
else
larger = value2;
cout << "Larger is: " << larger << endl;
Example: If-Else-1.cpp and If-Else-2.cpp (boolean, Char, etc.)
COMP103 - C++ Review

20. if-else-if Statements
Example: If-Else-If-1.cpp
COMP103 - C++ Review

21. if-else-if Statements
if <Mon, Wed>{
<goto COMP 103> }
else if <Tue>{
<goto Lab>
else if <12noon or 7PM>{
<eat>
else{
<sleep>
COMP103 - C++ Review

22. if-else-if Statement if(score >= 90)
cout << "Grade = A" << endl;
else if(score >= 80)
cout << "Grade = B" << endl;
else if(score >= 70)
cout << "Grade = C" << endl;
else if(score >= 60)
cout << "Grade = D" << endl;
else
cout << "Grade = F" << endl;
COMP103 - C++ Review

23. switch Statement Equivalent to the previous if-else-if
switch(score/10){
case 10:
case 9: cout << "Grade = A" << endl;
break;
case 8: cout << "Grade = B" << endl;
case 7: cout << "Grade = C" << endl;
case 6: cout << "Grade = D" << endl;
default: cout << "Grade = F" << endl; }
Example: Switch.cpp
COMP103 - C++ Review

24. Nested if Statements
Nested means that one complete statement is inside another
if <it's Monday>{
if <it's 1:00pm>{
if <it's raining>{
<bring umbrella> }
<go to COMP 103>
<call your friends>
COMP103 - C++ Review

25. “Dangling Else” Problem
What is the value of c after the following is executed?
int a=-1, b=1, c=1;
if(a>0)
if(b>0)
c = 2;
else
c = 3;
C++ groups a dangling else with the most recent if (answer: c=1).
Example: Dangling-Else.cpp
COMP103 - C++ Review

26. Programming
Functions
(Ch. 4)
COMP103 - C++ Review

27. Advantages of Functions
A complex problem is often easier to solve by dividing it into several smaller parts, each of which can be solved by itself.
These parts are called functions in C++
Functions make programs easier to understand.
Functions make programs easier to modify.
Functions can be called several times in the same program, allowing the code to be reused.
COMP103 - C++ Review

28. Function Input and Output
Result
Parameters
Example: Basic-Function.cpp
COMP103 - C++ Review

29. Functions in a Program C++ programs usually have the following form:
// include statements
// function prototypes
// main() function
// user-defined functions
COMP103 - C++ Review

30. Function Prototype
The function prototype declares the interface, or input and output parameters of the function, leaving the implementation for the function definition.
The function prototype has the following syntax:
<type> <function name>(<type list>);
Example: A function that prints the card (J) given the card number (11) as input:
void printcard(int num);
(This is a void function - a function that does not return a value)
COMP103 - C++ Review

31. Function Definition
The function definition can be placed anywhere in the program after the function prototypes.
You can place a function definition in front of main(). In this case there is no need to provide a function prototype for the function, since the function is already defined before its use.
A function definition has following syntax:
<type> <function name>(<parameter list>){
<local declarations>
<sequence of statements> }
COMP103 - C++ Review

32. Function Call A function call has the following syntax:
<function name>(<parameter list>)
There is a one-to-one correspondence between the parameters in a function call and the parameters in the function definition.
COMP103 - C++ Review

33. Printing Cards (void function)
The main() program which calls printcard()
#include <iostream>
using namespace std;
void printcard(int); // function prototype
int main(){
int c1, c2, c3, c4, c5;
// pick cards
. . .
// print cards
printcard(c1);
printcard(c2);
printcard(c3);
printcard(c4);
printcard(c5);
// find score
// print score }
COMP103 - C++ Review

34. Printing Cards
A function that prints the card (J) given the card number (11) as input:
void printcard(int cardnum){
if(cardnum==1)
cout << "A";
else if(cardnum>=2 && cardnum<=10)
cout << cardnum;
else if(cardnum==11)
cout << "J";
else if(cardnum==12)
cout << "Q";
else if(cardnum==13)
cout << "K"; }
COMP103 - C++ Review

35. Absolute Value (returns int)
#include <iostream>
int absolute(int x); // function prototype
int main(){
int x, y, diff;
cout << "Enter two integers: ";
cin >> x >> y;
diff = absolute(x - y);
cout << "The absolute diff is " << diff << endl;
return 0; }
// Define a function to take absolute value of an int
int absolute(int x){
if (x >= 0) return x;
else return -x;
Example: Basic-Function.cpp
COMP103 - C++ Review

36. Passing Parameters by Value
A function returns a single result (assuming the function is not a void function)
One of the statements in the function body should have the form:
return <expression>;
The value passed back by return should have the same type as the function.
Example: Basic-Function.cpp
COMP103 - C++ Review

37. Pass by Value
Different location in memory
Changes to the parameters inside the function body have no effect outside of the function.
COMP103 - C++ Review

38. Pass by Value: Example 1 For example, consider the following code:
int sum(int a, int b){
a = a + b;
return a; }
void main(){
int x, y, z;
x = 3; y = 5;
z = sum(x,y);
What is the value of x, y, and z at the end of the main() program?
Example: Pass-by-Value-1.cpp
COMP103 - C++ Review

39. Pass by Value: Example 1 The answer: 3, 5, and 8. (x,y,z)
Even though the value of parameter a is changed, the corresponding value in variable x does not change.
This is why this is called pass by value.
The value of the original variable is copied to the parameter, but changes to the value of the parameter do not affect the original variable.
In fact, all information in local variables declared within the function will be lost when the function terminates.
The only information saved from a pass by value function is in the return statement.
COMP103 - C++ Review

40. Pass by Value: Example 2 void Increment(int Number) {
Number = Number + 1;
cout << "Number =" << Number << endl; }
void main() {
int I = 10;
cout << "I is: " << I << endl;
Increment(I);
Output: 11; 10; 10
Example: Pass-by-Value-2.cpp
COMP103 - C++ Review

41. Passing Parameters by Reference
To have a function with multiple outputs, we have to use pass by reference.
Reference (address) of parameter is passed to the function, instead of its value.
If the function changes the parameter value, the changes will be reflected in the program calling it.
How to pass parameters by reference:
<type>& <variable>, ... , <type>& <variable>
COMP103 - C++ Review

42. Pass by Reference: Example
The correct implementation of the Increment function
#include <iostream>
using namespace std;
void Increment(int& Number){
Number = Number + 1;
cout << "Number: " << Number << endl; // 11 }
void main(){
int I = 10;
Increment(I);
cout << "I is: " << I << endl; // 11
Pass-by-Reference-1.cpp
Output : 11; 11
COMP103 - C++ Review

43. Example: Exchange two numbers
If we use pass by value, it will not work!!!
a and num1 are in the same location in memory
Also b and num2
COMP103 - C++ Review

44. Pass by value and by reference
COMP103 - C++ Review

45. Programming
Loops
(Ch. 6)
COMP103 - C++ Review

46. Iterative Constructs Provide Three constructs
Ability to control how many times a statement list is executed
Three constructs
while statement
for statement
do-while statement
COMP103 - C++ Review

47. The while Statement Syntax while (Expression) Action How it works:
If Expression is true then execute Action
Repeat this process until Expression evaluates to false
Action is either a single statement or a group of statements within braces
Expression
Action
true
false
Example: Factorial-while.cpp
COMP103 - C++ Review

48. Example: N! (while) int number, factorial, n;
cout << "Enter number: ";
cin >> number;
factorial = 1;
n = 1;
while(n <= number){
factorial *= n;
n++; }
cout << "The factorial of " << number
<< " is " << factorial << endl;
COMP103 - C++ Review

49. The for Statement Syntax for (ForInit; ForExpression; PostExpression)
Action
How it works:
Execute “ForInit” statement
As long as “ForExpression”
is true
Execute Action
Execute PostExpression
ForExpression
Action
true
false
ForInit
PostExpression
COMP103 - C++ Review

50. Example: N! (for) int number, factorial, n;
cout << "Enter number: ";
cin >> number;
factorial = 1;
for (n=1; n<=number; n++)
factorial *= n;
cout << "The factorial of " << number
<< " is " << factorial << endl;
Example: Factorial-For.cpp
COMP103 - C++ Review

51. The Do-While Statement
Syntax
do Action
while (Expression)
How it works:
Execute Action
if “Expression” is true then execute Action again
Repeat this process until Expression evaluates to false
Action is either a single statement or a group of statements within braces
Action
true
false
Expression
COMP103 - C++ Review

52. Example: N! (do-while) int number, factorial, n;
cout << "Enter number: ";
cin >> number;
factorial = 1;
n = 1;
do{
factorial *= n;
n++;
}while(n <= number);
cout << "The factorial of " << number
<< " is " << factorial << endl;
Example: Factorial-do-while.cpp
COMP103 - C++ Review

53. Which Loop to Use? For loop While loop Do-while loop
Usually best for sums, products, and counting loops.
While loop
You want to repeat an action without knowing exactly how many times it will be repeated.
There are situations when the action should not be executed.
Do-while loop
The action should always be executed at least once.
Otherwise, the do-while loops and while loops are used in similar situations.
COMP103 - C++ Review

54. How to Stop a Loop
Known number of iterations before the loop stops (for)
Test for a user-controlled
condition before or after
each iteration (while, do-while)
Use the break command.
COMP103 - C++ Review

55. Stop a loop: break
The break command is the same as the one used previously in switch.
break leaves the current loop immediately. It is recommended that break be used for situations where the loop needs to be terminated immediately (e.g., due to user intervention or if a fatal error occurs).
Use with care !!
COMP103 - C++ Review

56. Example: Maximum (while with break)
int value; //input value
int max=0; //maximum value
while(true){
cout << "Enter a value (-1 to stop): ";
cin >> value;
if(value > max)
max = value;
if(value==-1)
break; }
cout << "The maximum value found is "
<< " is " << max << endl;
MAX
COMP103 - C++ Review

57. Common Loop Errors while(balance != 0.0); {
balance = balance - amount; }
This will lead to an infinite loop!
for(n=1; n<=count; n++);
cout << "hello" << endl;
"hello" only printed once!
while(balance != 0.0){
balance may not become equal zero due to numerical inaccuracies
COMP103 - C++ Review

58. Nested Loops Nested loops are loops within loops.
// Program to output the
// multiplication table
int i; //Outer loop counter
int j; //Inner loop counter
for(i=1; i<=10; i++){
for(j=1; j<=10; j++)
cout << i*j << " ";
cout << endl; }
Example: Nested-For.cpp
Output …
COMP103 - C++ Review

59. Recursion (Ch.6, Section 6-9)
Programming
Recursion
(Ch.6, Section 6-9)
COMP103 - C++ Review

60. Recursion
Recursion is one way to decompose a task into smaller subtasks.
The smallest example of the same task has a non-recursive solution.
Example: The factorial function
n! = n * (n-1) * (n-2) * ... * 1 or
n! = n * (n-1)! and 1! = 1
A recursive solution may be simpler to write (once you get used to the idea) than a non-recursive solution.
But a recursive solution may not be as efficient as a non-recursive solution of the same problem.
Example: Factorial-Recursive.cpp
COMP103 - C++ Review

61. Recursion General Form
How to write recursively?
int rec(parameters){
if(stopping condition)
return stopping value;
value = rec(revised parameters);
return value; }
COMP103 - C++ Review

62. Example: N! Recursion int fac(int n){ int product; if(n <= 1)
return 1;
product = n * fac(n-1);
return product; }
void main(){
int number = 3;
cout << fac(number) << endl;
COMP103 - C++ Review

63. Execution trace fac(3) : 3 <= 1 ? No. product3 = 3 * fac(2)
1 <= 1 ? Yes.
return 1
product2 = 2 * 1 = 2
return product2
product3 = 3 * 2 = 6
return product3
fac(3) has the value 6
COMP103 - C++ Review

64. Programming
Arrays
COMP103 - C++ Review

65. Arrays
An array is a collection of data elements that are of the same type (e.g., a collection of integers, collection of characters, collection of doubles).
COMP103 - C++ Review

66. Arrays 1-dimensional array.
3-dimensional array (3rd dimension is the day).
Oct 15
Oct 16
Oct 14
COMP103 - C++ Review

67. Array Declaration – 1 Dimension
Syntax: <type> <arrayName>[<dimension>]
COMP103 - C++ Review

68. Subscripting – 1 Dimension
// array of 10 uninitialized ints
int A[10];
A[3] = 1;
int x = A[3]; 1 -- -- 1 A 4 5 6 3 2 8 9 7
A[4]
A[5]
A[6]
A[3]
A[0]
A[2]
A[8]
A[9]
A[7]
A[1]
COMP103 - C++ Review

69. Array Initialization – 1 Dimension
COMP103 - C++ Review

70. Example Definitions – 1 Dimension
Suppose
const int N = 20;
const int M = 40;
const int MaxStringSize = 80;
const int MaxListSize = 1000;
Then the following are all legal array definitions.
int A[10]; // array of 10 ints
char B[MaxStringSize]; // array of 80 chars
double C[M*N]; // array of 800 doubles
int Values[MaxListSize];// array of 1000 ints
COMP103 - C++ Review

71. Example: Smallest Value (1-dimension)
const int N=10;
int A[N];
int SmallestValueSoFar, i;
... // A[] is input by user
SmallestValueSoFar = A[0];
for (i=1; i<N; i++)
if (A[i] < SmallestValueSoFar)
SmallestValueSoFar = A[i];
Smallest
Example: 1D-MaxNum.cpp
COMP103 - C++ Review

72. 2-D Array Example int table[5][4]; COMP103 - C++ Review
Example: Mat-Add.cpp
COMP103 - C++ Review

73. Passing Arrays to Functions (Ch.8, p.388-397)
Programming
Passing Arrays to Functions
(Ch.8, p )
COMP103 - C++ Review

74. Passing Array Elements
Individual elements can be passed to a function like ordinary values.
COMP103 - C++ Review

75. Passing Arrays as Parameters
Arrays can be passed to functions in their entirety.
All that is required is the address of the first element and dimensions of the array.
The remainder of the array will be passed by reference automatically.
Using “[ ]” in the formal parameter specification indicates that the variable is an array.
COMP103 - C++ Review

76. Example: Multiple an array by 2
COMP103 - C++ Review

77. The const type modifier
If the function must not change any element of the array then const should be used in the formal parameter specification of that array.
COMP103 - C++ Review

78. Passing Multidimensional Arrays
How to pass a multidimensional array to a function:
void displayBoard(int b[][4]);
// function prototype requires variable name for arrays
void main(){
int board [4][4];
...
displayBoard(board); }
void displayBoard(int b[][4]){
// could also be: void displayBoard(int b[4][4]){
// but NOT: void displayBoard(int b[][]){
When passing a multidimensional array, only the size of the 1st dimension is optional, the 2nd, 3rd, etc. dimensions must be specified.
COMP103 - C++ Review

79. Programming Structures (Ch.11, p.567) COMP103 - C++ Review
Structtures: Chapter 11-8, pages
COMP103 - C++ Review

80. Structures
A structure is a collection of related data items, possibly of different types.
In C++, structure is a user defined type, called struct.
A struct is heterogeneous (of different types of data) whereas an array is homogeneous (of same type of data)
Examples:
Student record
student id, name, major, gender, start year, …
Bank account:
account number, name, currency, balance, …
Address book:
name, address, telephone number, …
In database applications, structures are called records.
COMP103 - C++ Review

81. struct basics Definition of a structure: Example: The “Date” structure
struct <struct-type>{
<type> <identifier_list>;
...
} ;
Example:
struct Date {
int day;
int month;
int year;
Each identifier defines a member of the structure.
The “Date” structure
has 3 members,
day, month & year.
COMP103 - C++ Review

82. struct examples Example: The “StudentRecord” structure has 4
struct BankAccount{
char Name[15];
int AcountNo[10];
double balance;
Date Birthday; };
struct StudentRecord{
int Id;
char Dept[5];
char Gender;
The “BankAcount” structure has simple, array and structure
types as members.
The “StudentRecord” structure has 4
members.
COMP103 - C++ Review

83. struct basics Declaration of a variable of struct type: Example:
<struct-type> <identifier_list>;
Example:
StudentRecord Student1, Student2;
Student1 and Student2 are variables of StudentRecord type.
Name
Id Gender
Dept
Name
Id Gender
Dept
Student1
Student2
COMP103 - C++ Review

84. Example 1: struct basics
The members of a struct type variable are accessed with the dot (.) operator:
<struct-variable>.<member_name>;
Example:
strcpy(Student1.Name, "Chan Tai Man"); Student1.Id = 12345; strcpy(Student1.Dept, "COMP"); Student1.gender = 'M'; cout << "The student is "; switch (Student1.gender){ case 'F': cout << "Ms. "; break; case 'M': cout << "Mr. "; break; } cout << Student1.Name << endl;
Student1
Name
Id Gender
Dept
Chan Tai Man M
COMP
COMP103 - C++ Review

85. Example 2: struct-to-struct assignment
The value of one struct type variable can be assigned to another variable of the same struct type.
Example:
strcpy(Student1.Name, "Chan Tai Man"); Student1.Id = 12345; strcpy(Student1.Dept, "COMP"); Student1.gender = 'M'; Student2 = Student1;
Student1
Chan Tai Man M
COMP
Chan Tai Man M
COMP
Student2
COMP103 - C++ Review

86. Example 3: Nested structures
We can nest structures inside structures.
Examples:
struct point{ double x, y; }; point P; struct line{ point p1, p2; }; line L; struct triangle{ point p1, p2, p3; }; triangle T;
(P.x, P.y)
(L.p2.x, L.p2.y)
(L.p1.x, L.p1.y)
(T.p2.x, T.p2.y)
(T.p3.x, T.p3.y)
(T.p1.x, T.p1.y)
COMP103 - C++ Review

87. Example 4: Nested structures
We can nest structures inside structures.
struct line{ point p1, p2; }; line L;
(L.p2.x, L.p2.y)
(L.p1.x, L.p1.y)
line
p p2
x y x y
COMP103 - C++ Review

88. Arrays of structures An ordinary array: One type of data
An array of structs: Multiple types of data in each array element. … …
COMP103 - C++ Review

89. Arrays of structures
Example: StudentRecord Class[100]; strcpy(Class[98].Name, "Chan Tai Man"); Class[98].Id = 12345; strcpy(Class[98].Dept, "COMP"); Class[98].gender = 'M'; Class[0] = Class[98];
Chan Tai Man M
COMP
. . . …
COMP103 - C++ Review

90. Arrays inside structures
We can use arrays inside structures.
Example: struct square{ point vertex[4]; }; square Sq;
Assign values to Sq using the given square
(4, 3)
(10, 3)
(4, 1)
(10, 1)
x y
x y
x y
x y
COMP103 - C++ Review