C++

Let's discover a new world !

c to C++

Many similar code

but C++ is not C, as C is not C++ !

Let's get into these differences ...

summary

Variables

I/O operators

New types

Control structures

Functions

Arrays

Pointers

Variables: Declaration

First way, the same as C language

type name = value;

int numberOfApples = 50;

Second way, only for C++

type name(value);

int numberOfBananas(32);

Both of them are correct,

but we will prefer the second one

Variables: Into the memory

int myAge(50);

This operation is actually composed of

Declaration (ask the computer for some memory space)
Initialization (put a value in that memory space)

Variables

Declare a variable without initializing it

int numberOfPlayers;
double score;

Variables

Modify the content of a variable

by a value

int a(0);a = 41;

by the content of another variable

int a(50);int b(23);a = b;

variables

constant: variable unmodifiable

double const pi(3.14);

Variables

Let's give another name to a variable: using a reference!

int myAge(50);
int& myAgeCopy(myAge);
printf("myAge = %i\n", myAge);printf("myAgeCopy = %i\n", myAgeCopy);

Why ?

Let's see that later when needed

I/O operators

No more printf and scanf

No more reasons to deal with %d, %i, %f, ...

Let's welcome the Input/Output operators !

I/O operators

Here is the default code proposed by Code::Blocks when creating a new C++ project:

#include <iostream>using namespace std;
int main(){  cout << "Hello world!" << endl;  return0;}

I/O OPERATORS

Cout is far easier to use than printf:

everything using "<<"

int myAge(50);cout << "myAge: " << myAge << endl;

No need for %d, %s, ... anymore !

I/O OPERATORS

Cin instead of scanf:

everything using ">>"

int myAge(0);cin >> myAge;

No need for %d, %s, ... anymore !

I/O operators

Input/Output example

#include <iostream>     using namespace std;
int main(){  int myAge;  cout << "How old are you?" << endl;  cin >> myAge;  cout << "Your Age: " << myAge << endl;  return 0;}

EXERCISE 1/2

Write a code executing the following result:

Welcome in our addition software!Enter a value for a:Enter a value for b:a + b =

Do not use C language, follow the C++ standards

Exercise 2/2

Complete your previous code by adding:

multiplication
division (quotient and remainder)

New types: string

C++ has a new type "string" to put text in it

string name = "Brice";

It works fine with cin and cout

NEW TYPEs: string

Using "string" example

#include <iostream>     using namespace std;
int main(){  string name("");  cout << "What is your name?" << endl;  cin >> name;  cout << "Hello " << name << ", how are you today?" << endl;  return 0;}

NEW TYPEs: bool

C++ has a new type "bool" to represent true or false

bool teacherIsGood(true);

Control structures

Programs needs to take decisions:

test variables (conditions)

repeat instructions several times (loops)

CONTROL STRUCTURES: CONDITIONS

"if" execute some instructions

if the condition is verified

unsigned int bananas(8); // unsigned: positive integer if (bananas < 5){  cout << "You need to buy some bananas" << endl;}

CONTROL STRUCTURES: CONDITIONS

"if ... else" execute some instructions

if the condition is or is not verified

unsigned int bananas(8); // unsigned: positive integer if (bananas < 5){  cout << "You need to buy some bananas" << endl;}else{  cout << "You have enough bananas" << endl;}

CONTROL STRUCTURES: CONDITIONS

"if ... else if ... else" add another test

unsigned int bananas(8); // unsigned: positive integer if (bananas <= 10 && bananas >= 3){  cout << "Do not forget to eat your bananas" << endl;}else if (bananas < 3){  cout << "You need to buy some new bananas" << endl;}else {  cout << "You bought to much bananas" << endl;}

CONTROL STRUCTURES: conditions

Tip: test several values using "switch"

unsigned int numberOfBananas(10);
switch (numberOfBananas){  case 1: // if    cout << "You still have 1 banana" << endl;    break;  case 2: // else if    cout << "You still have 2 bananas" << endl;    break;  [...] // else if ... else if ... else if ...  default: // else    cout << "You still have "<< numberOfBananas << "bananas" << endl;    break;}

CONTROL STRUCTURES: CONDITIONS

Specific case: booleans

bool man(true)
if (man){  cout << "You are a man" << endl;}else{  cout << "You are a woman" << endl;}

CONTROL STRUCTURES: LOOPS

"while" and "do ... while" execute instructions again and again

as long as a condition is verified

Difference?

"while" checks the condition and execute instructions

"do ... while" execute instructions and checks the condition

CONTROL STRUCTURES: Loops

int numberOfBananas; // int is signed (can be negative)
cout << "How many bananas do you have? ";cin >> numberOfBananas;
while (numberOfBananas < 0){  cout << "Enter a correct number of bananas";  cin >> numberOfBananas;}
cout << "You have " << numberOfBananas << " bananas" << endl;

CONTROL STRUCTURES: Loops

int numberOfBananas; // int is signed (can be negative)
cout << "How many bananas do you have? ";cin >> numberOfBananas;

do{  cout << "Enter a correct number of bananas";  cin >> numberOfBananas;}while (numberOfBananas < 0);

cout << "You have " << numberOfBananas << " bananas" << endl;

CONTROL STRUCTURES: LOOPS

"for" executes instructions n times

declaration and initialization of a counter
condition
modification of the counter

for (init counter; condition; modif counter){  [...]  instruction;  [...]}

CONTROL STRUCTURES: LOOPS

int numberOfBananas(10);
for (int i(0); i < numberOfBananas; i++){  cout << "I ate " << i << " bananas" << endl;}

I ate 0 bananasI ate 1 bananasI ate 2 bananas...I ate 9 bananas

Functions

Here is the default code proposed by Code::Blocks when creating a new C++ project. This code already contain a function: main()

#include <iostream>using namespace std;
int main() // Every C++ programs start by running this function{  cout << "Hello world!" << endl;  return0;}

functions

Cut the code in smaller parts

Use some instructions several times

A function:

Can receive datas (arguments)
Process its instructions
Return a value as a result

Functions: skeleton

type functionName(arguments){  [...]  instructions;  [...]
  return value;}

Functions: add()

int add(int a, int b){  int result;  result = a + b;  return result;}
int main(){  cout << "Write a first integer: "; cin >> int1;  cout << "Write a second integer: "; cin >> int2;  int int3 = add(int1, int2);  cout << int1 << "+" << int2 << "=" << int3 << endl;  return 0;}

Functions: void

"void" allows the creation of a function

without a return value

void sayHello(){  cout << "Hello!" << endl;}

Functions: calls

Call by value:

data copied into a local variable

Call by reference:

local variable point to the original data

Functions: call by value

int addTwo(int a){  a = a + 2;  return a;}
int main(){  int number(6), result;  result = addTwo(number);  cout << "number=" << number << " and result=" << result << endl;  return 0;}
// number = 6// result = 8

Functions: call by reference

int addTwo(int& a){  a = a + 2;  return a;}
int main(){  int number(6), result;  result = addTwo(number);  cout << "number=" << number << " and result=" << result << endl;  return 0;}
// number = 8// result = 8

FUNCTIONS: CALL BY CONST REFERENCE

Faster: avoid copy

Safer: prevent modifications

void copyBook(string text) // long to copy{}
void copyBook2(string& text) // can modify original text{}
void copyBook3(string const& text) // fast copy and read-only{}

Functions: ORDERING the code

Every functions in one file ...

BAD HABIT !!!

Sort the code using several files

Functions: ordering the code

As an example, let's group all the mathematics functions.

2 files are needed:

math.h (header file) containing functions prototypes
math.cpp (source file) containing functions implementations

functions: ORDERING THE CODE

math.h

#ifndef MATH_H_INCLUDED // Ensure to include this file only once#define MATH_H_INCLUDED // in the compilation process
// Add 2 numbers and return their sum
int add(int a, int b);
// Take number as argument and return number + 2
int addTwo(int a); 
#endif

Advice: always comment the aim of the functions

functions: ORDERING THE CODE

math.cpp

#include "math.h" // Link the header
int add(int a, int b){  int result;  result = a + b;  return result;}
int addTwo(int a){  a = a + 2;  return a;}

Functions: ORDERING THE CODE

main.cpp

#include <iostream>#include "math.h" // Link the functions of math files
int main(){  int number;  cout << "Enter an integer: "; cin >> number;  addTwo(number);  cout << "Your number + 2 = " << number << endl;
  return 0;}

Arrays

Group datas of same type together

Static arrays

Dynamic arrays

Multidimensional array

Arrays: static

The size of the array is known:

it book the exact memory space

Skeleton

 type name[size];

Example: declare an array of 5 classes

int const numberOfClasses(5); // The size of the array is knownstring classes[numberOfClasses];

ARRAYS: STATIC

Fill the array

string classes[5];
classes[0] = "B1"; // Arrays starts with the index 0classes[1] = "B2";
classes[2] = "B3";
classes[3] = "M1";
classes[4] = "M2";

ARRAYS: STATIC

Read a value

cout << "The class for B2 students is: " << classes[1] << endl;

Run through all the array

for(int i=0; i<numberOfClasses; i++) // numberOfClasses = 5{  cout << classes[i] << endl;}

Arrays: dynamic

The size of the array can change

#include <vector> // Do not forget to include the "vector" library!

Skeleton

vector<type> name(initialSize, defaultValue);

Examples

vector<double> scores;vector<string> students(5);vector<string> teachers(10, "no name");

ARRAYS: DYNAMIC

Fill the array

vector<string> students(5, "no name");

students[0] = "Justin BIEBER";students[1] = "Bruce LEE";students[2] = "Jack JOHNS";

Read it

cout << students[1] << endl; // Display Bruce LEEfor (int i=0; i<students.size(); i++) //size() returns the array size{  cout << students[i] << endl;} // Display all the students names

arrays: Dynamic

Add a value at the end of the array

vector<double> scores; // Declare an empty array
scores.push_back(18);scores.push_back(11);
for(int i=0; i<scores.size(); i++) { cout << scores[i] << endl; }

Result:

arrays: Dynamic

Remove the last value of the array

vector<double> scores; // Declare an empty array
scores.push_back(18); // Add the value 18scores.push_back(11); // Add the value 11
scores.pop_back(); // Remove the last value of the array
for(int i=0; i<scores.size(); i++) { cout << scores[i] << endl; }

Result:

Arrays: multidimensional

An array of arrays

Skeleton

type name[sizeA][sizeB]...[sizeN];

Example

int const sizeX(5);int const sizeY(4);int scores[sizeX][sizeY];

Exercise

Write a program that asks the user to type 10 integers of an array.

The program must output the largest element in the array,

and the index at which that element was found (if the largest element appear several times, output all its indexes).

POINTERS

Each memory space in a computer can contain only

one variable, and has an address

A variable can be accessed

by its name
by its address

int myAge(30);cout << "The value of myAge is: " << myAge << endl;cout << "The address of myAge is: " << &myAge << endl;

Pointers

How to record an address and access to its value?

Using a pointer!

A pointer is a variable containing the address of another variable

Pointers: Declaration

Skeleton

type *name;

"type" must be the same type as the variable pointed to

Examples

int *p1;double *p2;sting *p3;unsigned int *p4;vector<string> *p5;

Pointers: declaration

ATTENTION !!!

If the pointer does not point to any known address

DANGER -> it could point to a system variable

Prevention

Always give the value 0 to the pointer when declaring it

type *name(0);

Example

int *p1(0);

POINTERS: INITIALIZATION

Store an address into the pointer

int myAge(30);int *myPointer(0);
myPointer = &myAge;

POINTER: USE

Display its content (an address)

cout << myPointer << endl; // Output 0x1ab23c4d for example

Display the value pointed to

cout << *myPointer << endl; // Output 30