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1. 1
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2. 2
A C++ program
//if necessary include headers
//#include <foo.h>
void main() {
//variable declaration
//read values input from user
//computation
//print output to user
}
Notes:
 what follows after // on the same line is considered comment
 indentation is for the reader; compiler ignores all spaces and new
line ; the delimiter for the compiler is the semicolon
 all statements ended by ;

3. 3
Identifiers
 Rules:
 Names begin with alphabetic character
including an underscore e.g. get_Name,
_Name, a_type
 Variables- Case sensitive
 Lower vs. upper case matters!!
 Void is different than void
 Main is different that main
Initialization can be done at the beginning e.g.
int m=10;

4. 4
Example
When learning a new language, the first program people
usually write is one that salutes the world :)
Here is the Hello world program in C++.
#include <iostream.h>
int main() {
cout << “Hello world!”;
return 0;
}

5. 5
Variable declaration
type variable-name;
Meaning: variable <variable-name> will be a variable of type
<type>
Where type can be:
 int //integer
 double //real number
 char //character
 Long int // 32 bits
 Float // floating point numbers
Example:
int a, b, c;
double x;
int sum;
char my-character;

6. 6
Input statements
cin >> variable-name;
Meaning: read the value of variable <variable-name>
from the user
Example:
cin >> a;
cin >> b >> c;
cin >> x;
cin >> my-character;

7. 7
Output statements
cout << variable-name;
Meaning: print the value of variable <variable-name> to the user
cout << “any message “;
Meaning: print the message within quotes to the user
cout << endl;
Meaning: print a new line
Example:
cout << a;
cout << b << c;
cout << “This is my character: “ << my-character << “ he he he”<< endl;

8. 8
If statements
if (condition) {
S1;
}
else {
S2;
}
S3;
True False
condition
S1 S2
S3

9. 9
Boolean conditions
..are built using
 Comparison operators
== equal
!= not equal
< less than
> greater than
<= less than or equal
>= greater than or equal
 Boolean operators
&& and
|| or
! not

10. 10
Examples
Assume we declared the following variables:
int a = 2, b=5, c=10;
Here are some examples of boolean conditions we
can use:
 if (a == b) …
 if (a != b) …
 if (a <= b+c) …
 if(a <= b) && (b <= c) …
 if !((a < b) && (b<c)) …

11. 11
If example
#include <iostream.h>
void main() {
int a,b,c;
cin >> a >> b >> c;
if (a <=b) {
cout << “min is “ << a << endl;
}
else {
cout << “ min is “ << b << endl;
}
cout << “happy now?” << endl;
}

12. 12
While statements
while (condition) {
S1;
}
S2;
True False
condition
S1
S2

13. 13
While example
//read 100 numbers from the user and output their sum
#include <iostream.h>
void main() {
int i, sum, x;
sum=0;
i=1;
while (i <= 100) {
cin >> x;
sum = sum + x;
i = i+1;
}
cout << “sum is “ << sum << endl;
}

14. 14
Arrays
Used to store a collection of elements (variables)
type array-name[size];
Meaning:
This declares a variable called <array-name> which contains
<size> elements of type <type>
The elements of an array can be accessed as: array-name[0],
…array-name[size-1]
Example:
int a[100]; //a is a list of 100 integers, a[0], a[1], …a[99]
double b[50];
char c[10];

15. 15
Array example
//Read 100 numbers from the user
#include <iostream.h>
void main() {
int i, a[100], n;
i=0; n=100;
while (i<n) {
cout << “Input element “ << i << “: ”;
cin >> a[i];
i = i+1;
}
//do somehing with it ..
}

16. 16
Exercises
Write a C++ program to read a sequence of (non-negative)
integers from the user ending with a negative integer and
write out
 the average of the numbers
 the smallest number
 the largest number
 the range of the numbers (largest - smallest)
 Example:
 The user enters: 3, 1, 55, 89, 23, 45, -1
 Your program should compute the average of {3, 1, 55, 89, 23,
45} etc

17. 17
Exercises
 Write a program that asks the user
 Do you want to use this program? (y/n)
 If the user says ‘y’ then the program
terminates
 If the user says ‘n’ then the program asks
 Are you really sure you do not want to use this program? (y/n)
 If the user says ‘n’ it terminates, otherwise it prints
again the message
 Are you really really sure you do not want to use this program?
(y/n)
 And so on, every time adding one more “really”.

18. 18
Pointers
int *intPtr;
intPtr = new int;
*intPtr = 6837;
delete intPtr;
int otherVal = 5;
intPtr = &otherVal;
Create a pointer
Allocate memory
Set value at given address
*intPtr 6837
intPtr 0x0050
Change intPtr to point to
a new location
*intPtr 5
intPtr 0x0054
otherVal
&otherVal
Deallocate memory

19. 19
Arrays
Stack allocation
int intArray[10];
intArray[0] = 6837;
Heap allocation
int *intArray;
intArray = new int[10];
intArray[0] = 6837;
...
delete[] intArray;

20. 20
Strings
A string in C++ is an array of characters
char myString[20];
strcpy(myString, "Hello World");
Strings are terminated with the NULL or '0' character
myString[0] = 'H';
myString[1] = 'i';
myString[2] = '0';
printf("%s", myString);
output: Hi

21. Prevents multiple references
21
Class Basics
#ifndef _IMAGE_H_
#define _IMAGE_H_
#include <assert.h>
#include "vectors.h“
class Image {
public:
...
private:
...
};
#endif
Include a library file
Include a local file
Variables and functions
accessible from anywhere
Variables and functions accessible
only from within this class

22. 22
C++ Functions
Predefined Functions
 C++ comes with libraries of predefined
functions
 Example: sqrt function
 the_root = sqrt(9.0);
 returns, or computes, the square root
of a number
 The number, 9, is called the argument
 the_root will contain 3.0
3.2

23. 23
Function Calls
 sqrt(9.0) is a function call
 It invokes, or sets in action, the sqrt function
 The argument (9), can also be a variable or an
expression
 A function call can be used like any
expression
 bonus = sqrt(sales) / 10;
 Cout << “The side of a square with area “ <<
area
<< “ is “ << sqrt(area);

24. 24
Function Call Syntax
 Function_name (Argument_List)
 Argument_List is a comma separated list:
(Argument_1, Argument_2, … , Argument_Last)
 Example:
 side = sqrt(area);
 cout << “2.5 to the power 3.0 is “ << pow(2.5, 3.0);

25. 25
Function Libraries
 Predefined functions are found in libraries
 The library must be “included” in a program
to make the functions available
 An include directive tells the compiler which
library header file to include.
 To include the math library containing sqrt():
#include <cmath>
 Newer standard libraries, such as cmath, also
require the directive using namespace std;

26. 26
Other Predefined Functions
 abs(x) --- int value = abs(-8);
 Returns absolute value of argument x
 Return value is of type int
 Argument is of type x
 Found in the library cstdlib
 fabs(x) --- double value = fabs(-8.0);
 Returns the absolute value of argument x
 Return value is of type double
 Argument is of type double
 Found in the library cmath

27. 27
Type Casting
 Look at this problem with integer division:
int total_candy = 9, number_of_people = 4;
double candy_per_person;
candy_per_person = total_candy / number_of_people;
 candy_per_person = 2, not 2.25!
 A Type Cast produces a value of one type
from another type
 static_cast<double>(total_candy) produces a double
representing the integer value of total_candy

28. 28
Type Cast Example
 int total_candy = 9, number_of_people = 4;
double candy_per_person;
candy_per_person = static_cast<double>(total_candy)/
number_of_people; candy_per_person now is 2.25!
 This would also work:
candy_per_person = total_candy /
static_cast<double>( number_of_people);
 This would not!
candy_per_person = static_cast<double>( total_candy /
number_of_people);
Integer division occurs before type cast

29. 29
Exercise
 Can you
 Determine the value of d?
double d = 11 / 2;
 Determine the value of
pow(2,3) fabs(-3.5), sqrt(pow(3,2))
7 / abs(-2),ceil(5.8),floor(5.8)
 Convert the following to C++
x + y xy+7
b b ac
- + 2 - 4
a
2

30. 30
Programmer-Defined Functions
 Two components of a function definition
 Function declaration (or function prototype)
 Shows how the function is called
 Must appear in the code before the function can be called
 Syntax:
Type_returned Function_Name(Parameter_List);
//Comment describing what function does
 Function definition
 Describes how the function does its task
 Can appear before or after the function is called
 Syntax:
Type_returned Function_Name(Parameter_List)
{
//code to make the function work
}
;
3.3

31. 31
Function Declaration
 Tells the return type
 Tells the name of the function
 Tells how many arguments are needed
 Tells the types of the arguments
 Tells the formal parameter names
 Formal parameters are like placeholders for the actual
arguments used when the function is called
 Formal parameter names can be any valid identifier
 Example:
double total_cost(int number_par, double price_par);
// Compute total cost including 5% sales tax on
// number_par items at cost of price_par each

32. 32
Function Definition
 Provides the same information as the declaration
 Describes how the function does its task
 Example:
function header
double total_cost(int number_par, double price_par)
{
const double TAX_RATE = 0.05; //5% tax
double subtotal;
subtotal = price_par * number_par;
return (subtotal + subtotal * TAX_RATE);
}
function body

33. 33
The Return Statement
 Ends the function call
 Returns the value calculated by the function
 Syntax:
return expression;
 expression performs the calculation
or
 expression is a variable containing the
calculated value
 Example:
return subtotal + subtotal * TAX_RATE;

34. 34
The Function Call
 Tells the name of the function to use
 Lists the arguments
 Is used in a statement where the
returned value makes sense
 Example:
double bill = total_cost(number, price);

35. 35
Function Call Details
 The values of the arguments are plugged into
the formal parameters (Call-by-value
mechanism with call-by-value parameters)
 The first argument is used for the first formal
parameter, the second argument for the second
formal parameter, and so forth.
 The value plugged into the formal parameter is used
in all instances of the formal parameter in the
function body

36. 36
Alternate Declarations
 Two forms for function declarations
1. List formal parameter names
2. List types of formal parmeters, but not names
 First aids description of the function in comments
 Examples:
double total_cost(int number_par, double price_par);
double total_cost(int, double);
 Function headers must always list formal
parameter names!

37. 37
Order of Arguments
 Compiler checks that the types of the arguments
are correct and in the correct sequence.
 Compiler cannot check that arguments are in the
correct logical order
 Example: Given the function declaration:
char grade(int received_par, int min_score_par);
int received = 95, min_score = 60;
cout << grade( min_score, received);
 Produces a faulty result because the arguments are not in
the correct logical order. The compiler will not catch this!

38. 38
Function Definition Syntax
 Within a function definition
 Variables must be declared before they
are used
 Variables are typically declared before
the executable statements begin
 At least one return statement must end
the function
 Each branch of an if-else statement might
have its own return statement

39. 39
Placing Definitions
 A function call must be preceded by either
 The function’s declaration
or
 The function’s definition
 If the function’s definition precedes the call, a
declaration is not needed
 Placing the function declaration prior to the
main function and the function definition
after the main function leads naturally to
building your own libraries in the future.

40. 40
Parameter Passing
pass by value
int add(int a, int b) {
return a+b;
}
int a, b, sum;
sum = add(a, b);
pass by reference
int add(int *a, int *b) {
return *a + *b;
}
int a, b, sum;
sum = add(&a, &b);
Make a local copy of a & b
Pass pointers that reference
a & b. Changes made to a
or b will be reflected
outside the add routine

41. 41
Parameter Passing
pass by reference – alternate notation
int add(int &a, int &b) {
return a+b;
}
int a, b, sum;
sum = add(a, b);

42. 42
Exercise
 Can you
 Write a function declaration and a function definition
for a function that takes three arguments, all of type
int, and that returns the sum of its three arguments?
 Describe the call-by-value parameter mechanism?
 Write a function declaration and a function definition
for a function that takes one argument of type int and
one argument of type double, and that returns a value
of type double that is the average of the two
arguments?

43. 43
Good sites
 http://www.cs.ucr.edu/cs10/cs10_03fal/slides/