2.overview of c++ ________lecture2

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A quick introduction to C++ A quick introduction to C++

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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 ;

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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;

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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;

}

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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;

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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;

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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;

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If statements

if (condition) {S1;

}else {

S2;}S3;

condition

S1 S2

S3

True False

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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

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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)) …

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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;}

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While statements

while (condition) {S1;

}S2;

condition

S1

S2

True False

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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;}

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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];

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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 ..}

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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

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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”.

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Pointers

int *intPtr;

intPtr = new int;

*intPtr = 6837;

delete intPtr;

int otherVal = 5;intPtr = &otherVal;

Create a pointerAllocate memory

Set value at given address

Change intPtr to point toa new location

6837*intPtr

0x0050 intPtr

5*intPtr

0x0054 intPtr

otherVal

&otherVal

Deallocate memory

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Arrays

int intArray[10];intArray[0] = 6837;

int *intArray;intArray = new int[10];intArray[0] = 6837;

...

delete[] intArray;

Stack allocation

Heap allocation

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Strings

char myString[20];strcpy(myString, "Hello World");

myString[0] = 'H';myString[1] = 'i';myString[2] = '\0';

printf("%s", myString);

A string in C++ is an array of characters

Strings are terminated with the NULL or '\0' character

output: Hi

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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

Prevents multiple references

Variables and functionsaccessible from anywhere

Variables and functions accessibleonly from within this class

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C++ FunctionsPredefined 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

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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);

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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);

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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;

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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

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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

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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

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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++

yx + xy 7+

a

acbb

2

42 −+−

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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

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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 actualarguments 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

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Function Definition

Provides the same information as the declaration Describes how the function does its task

Example:

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 header

function body

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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;

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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);

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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 secondformal parameter, and so forth.

The value plugged into the formal parameter is usedin all instances of the formal parameter in the function body

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Alternate Declarations

Two forms for function declarations1. List formal parameter names2. 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!

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Order of Arguments

Compiler checks that the types of the argumentsare correct and in the correct sequence.

Compiler cannot check that arguments are in thecorrect 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!

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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

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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 definitionafter the main function leads naturally to building your own libraries in the future.

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Parameter Passing

int add(int a, int b) { return a+b;}

int a, b, sum;sum = add(a, b);

pass by value

int add(int *a, int *b) { return *a + *b;}

int a, b, sum;sum = add(&a, &b);

pass by reference

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

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Parameter Passing

int add(int &a, int &b) { return a+b;}

int a, b, sum;sum = add(a, b);

pass by reference – alternate notation

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Exercise Can you

Write a function declaration and a function definitionfor a function that takes three arguments, all of typeint, 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?

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Good sites

http://www.cs.ucr.edu/cs10/cs10_03fal/slides/