C++ Overview

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History

Started in 1983
Improved on the C language
Data Abstraction
OOP

C++ language

Slower than C but faster than Java
relatively clean language
objects to structure

Basic types

int
double or long double
char
bool

Variables

Syntax type v;

int p = 25

Strings

string t ; define t as a variable... – string word = "hello" ; – s.size() represents the length of s – s[i] is the i-th character of s ( i = 0,1,. . . s.size()-1) – s+t is a new string corresponding to concatenation of s and t

string ch1 ; /* construction of an empty string : ch1.size() == 0 */
string ch2 (10, ’*’) ; /* construction of 10 characters string equal to ’*’ */
/* ch2.size() == 10 */
string ch3 (5, ’\0’) ; /* construction of 5 characters string with zero code */
/* ch2.size() == 5 */

Arrays

int tab[5] = { 10, 20, 5, 0, 3 } // an array of 5 int with values 10, 20, 5, 0 and 3
int tab[] = { 10, 20, 5, 0, 3 } // an array of dimension 5
int tab[5] = { 10, 20 } ; // equivalent to tab[] = {10, 20, 0, 0, 0}
int tab[5] = { 10, 20, 5 } ; // equivalent to tab[] = {10, 20, 5, 0, 0} 
// Multidimensional
int tab[3][4] = { //three elements; each element is an array of size 4
{ 1, 2, 3, 4 } , // initializers for the row indexed by 0
{ 5, 6, 7, 8 }, // initializers for the row indexed by 1
{ 9,10,11,12 } // initializers for the row indexed by 2
};
- The nested braces are optional. The following initialization is equivalent :
int tab[3][4] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 } ;
- At each of the two levels, the last values can be omitted.
- The following statements are correct (but not equivalent) :
int tab[3][4] = { { 1, 2 } , { 3, 4, 5 } } ;
int tab[3][4] = { 1, 2 , 3, 4, 5 } ;

Initializers and allocation class

Initializers that can be used for elements of an array follow the same rules as the initializers of the scalar variables, i.e. :

For a static array, Initialization values must be constant expressions of a type compatible by assignment with the type of elements in the array; static variables or automatic variables declared with the const attribute can be shown.

void f()
{ 
    const int N = 10 ;
    static int delta = 3 ;
    .....
    int tab[5] = { 2*N-1, N-1, N, N+1, 2*N+1} ;
    int t[3] = { 0, delta, 2*delta } ;
}

For an automatic array, you can use any expression of a type compatible by assigning to the type of elements in the array.

const int NEL = 10 ;
void fct (int p)
{ 
    int n ;
    .....
    int tab[] = {NEL, p, 2*p, n+1, n+p} ;
    .....
}

We can also use the vector class, for this you have to place at the top of the file.

# include <vector>
//– An array is typed :
vector<int> Tab(100 , 5) ;
vector<int> Tab(50) ;
vector<double> T ;
//– General structure :
vector<type> Name(n, v) ;
vector<type> Name1 = Name2 ;
//– Values of Name2 are then copied into Name1.
//– T.size() is the size of T.
//NB: size() actually returns an unsigned Integer, its exact type is vector<type> :: size_type
//– T[i] refers to the i-th element with i = 0, . . . T.size()-1.
vector<vector<int> > T define a two dimensions array.
//To initialize it, you can use the following statement :
vector<vector<int> >T2
T2(100,vector<int>(50,1)) ;
//We initialize each of the 100 elements of T2 with an array of size 50 filled with 1

Expression:

The expression ++var increments the variable var and returns the new value. (++i is equivalent to i=i+1)

The expression var++ increments the variable var and returns the the old value. (i++ is equivalent to (i=i+1)-1).
n = i++ - 5 will affect the value 6 to i and value 0 to n (because here the value of the expression i++ is 5).

Loops

For Loop

for (expr1 ;expr2 ;expr3) instr

for(i=0 ; i<235 ;i=i+1) cout << T[i] ;
for(i=0, j=1 ; i<235 ;i=i+1,j=j+3) cout << T[i][j] ;

While Loop

while (expr) instr

Do While Loop

do instr while (expr) ;

Input/Output

Add #include <iostream>

Syntax : cout < < expr1 < < . . . < < exprn ; This statement prints expr1 then expr2

cout (or std::cout) means the standard “Output”
<< is a binary operator. It is associative from left to right – the second operand is the expression to be displayed – The result is “Output stream type
<< is overloaded (or over-defined): the same operator is used to display characters, integers, real characters or strings of characters etc.
Displaying a line break is done by means of cout << endl

Read on the keyboard

Syntax : cin > > var1 > > . . . > > varn ; This statement reads (keyboard) values and assigns them to var1 then var2 . . .

cin is the standard input stream, and >> is an operator similar to <<.
The characters typed on the keyboard are recorded in a buffer in which the cin come to draw values. Spaces, tabulations and line ends are separators.

Program structure

#include <iostream>
void test(int j) {cout << j << endl ; }
int main()
{
    int i =20 ;
    cout << " Hello" << endl ;
    test(i) ;
    return 0;
}

Functions

int k=34, t=5, m ;
m = max(k,2*t+5) ;
int max(int a,int b)
{ 
    int res=b ;
    if (a>b) res = a ;
    return res ; 
}
...
main()
{
    int x, y ;
    x=5 ;
    y=10 ;
    int z = max(y, x) ;
    cout<<" z = "<<z ;
}

Displaying the contents of an array of integers

void DisplayTab(vector<int> T)
{
    int i ;
    for (i=0 ; i< T.size() ; i++)
    cout << T[i] << " " ;
}

Entering an array of integers

vector<int> EnterTab()
{
    int size ;
    cout << " Enter a size : " ;
    cin >> size ;
    vector<int> res(size,0) ;
    for (int i=0 ; i<size ; i++) {
        cout << " val = " ;
        cin >> res[i] ;
    }
    return res ;
}

Searching for the greatest element

int Search(vector<int> T)
{
    if (T.size()==0) {
        cout << " Error ! Array empty !" << endl ;
        return -1 ;
    }
    int res=T[0] ;
    for (int i=1 ; i<T.size() ;i++)
        if (T[i] > res) res=T[i] ;
        return res ;    
}

Programming Concepts with C++

Pointers