jrtechs-NodeJSBlog/entries/programming/c-to-c++-tutorial.md

Namespaces

Input/Output

using namespace std;
#include <iostream>

int main()
{
    cout << "Hello World" << endl;   
    
    int a;
    cin << a;
    
    cout << "You entered: << a << endl;
    
    return 0;
}

Global Variable

using namespace std;
#include <iostream>

double bar = 64;

int main ()
{
   double bar = 12;

   cout << "Local bar:  " << bar << endl;
   cout << "Global bar: " << ::bar << endl;

   return 0;
}

Multiple Names for a Variable/Aliasing

double pi = 3.145;
double &x = pi;  //pi is x

x = 2.1;

cout << "pi: " << pi << " x: " << x << endl; // prints pi: 2.1 x: 2.1

Passing Variables by Reference

void change (double &r, double s)
{
   r = 100;
   s = 200;
}

int main()
{
    int x = 1;
    int y = 2;
    cout << x << ", " << y << endl;
    change(x, y);
    cout << x << ", " << y << endl;
    
    return 0;
}

Same code in C.

void change(double *r, double s)
{
    *r = 100;
    s = 200;
}

int main()
{
    int x = 1;
    int y = 2;
    printf("%d, %d", x, y);
    change(&x, y);
    printf("%d, %d", x, y);
    
    return 0;
}

Functions Returning Variables not Values

A reference can be used to have a function return a variable -- not a value.

using namespace std;
#include <iostream>

int &smallest (int &x, int &y)
{
    if (x < y) 
        return x;
    else
        return y;
}

int main ()
{
    int k = 33;
    int m = 2;
    
    cout << "k: " << k << " m: " << m << endl; // prints k: 33 m: 2
    
    smallest (k, m) = 10;
    
    cout << "k: " << k << " m: " << m << endl; // prints k: 33 m: 10
    
    return 0;
}

Namespaces

namespace foo
{
    int a, b;
}


int main()
{
    first::a = 2;
    
    return 0;
}

Inline -- similar to Macros

Inline can be used to replace a function which contains very simple logic -- no for loops, etc. Like a macro, this will be inserted everywhere the code is used; a draw back to inline methods is that the compiled source will be larger. But, they typically run faster.

inline int square(int x)
{
    return x * y;
}

int main()
{
    int k = 4;
    
    cout << square(k) << endl; //prints 4
    
    return 0;
}

Exceptions

int x;
cout << "Type a number: ";
cin >> x;
cout << endl;

try
{
    if(a > 150)
        throw 150;
    if(a < 15)
        throw 15;
    throw a % 2;
}
catch(int result)
{
    cout << result << " was thrown." << endl;
}

Default Parameters for Functions

double multiply(double x, double y = 5)
{
    return x * y;
}

int main()
{
    cout << multiply(4) << endl; // 20
    cout << multiply(4, 4) endl; // 15
    
    return 0;
}

Function Overloading

double add(double x)
{
    return x + x;
}

double add(double x, double y)
{
    return x + y;
}

int add(int x, int y)
{
    return x + y;
}

int main()
{
    cout << multiply(4) << endl; // 20
    cout << multiply(4, 4) endl; // 15
    
    return 0;
}

Operator Overloading

using namespace std;
#include <iostream>

struct tuple
{
   int x;
   int y;
};

tuple operator + (int a, vector b)
{
   vector r;

   r.x = a + b.x;
   r.y = a + b.y;

   return r;
}

int main ()
{
   tuple k, m;              // No need to type "struct tuple"
                            // also no need to typedef
   k.x = 3;
   k.y = 6;

   m = 2 + k;               // Voodoo witchcraft

   cout << "(" << m.x << ", " << m.y << ")" << endl;

   return 0;
}

Functions with Generic Parameter Types

template <class ttype>
ttype max (ttype a, ttype b)
{
   ttype r;

   r = a;
   if (b < a) r = b;

   return r;
}



template <class type1, class type2>
type1 maximum (type1 a, type2 b)
{
    type1 r, b_converted;
    r = a;
    b_converted = (type1) b;
    if (b_converted > a) 
        r = b_converted;
    return r;
}

Replacement for malloc and free

int i*;
i = new int;
*i = 55;
delete i;

i = new int[15];
i[0] = 99;
delete i;

Struct Functions

struct tuple
{
    int i;
    int x;

    int sum()
    {
        return i + x;
    }
};

Classes

class Tuple
{
public:
    int i;
    int x;

    int sum()
    {
        return i + x;
    }
};

Class Constructor and De-constructor

class Tuple
{
public:
    int i;
    int x;
    
    Tuple(int i1, int i2)
    {
        i = i1;
        x = i2;
    }
    
    ~Tuple()
    {
        //delete any memory you have!
    }

    int sum()
    {
        return i + x;
    }
};


// in main


Tuple t (12, 14);

Tuple tt = new Tuple(12, 15);

Scope

class Person
{
protected:
    int age;
    string name;    
    
public:
    Person(int age, string name)
    {
    }
    
    ~Person()
    {
    }
    
private:
    void increaseAge()
    {
        age++;
    }
}

This keyword

class Person
{
protected:
    int age;
    string name;    
    
public:
    Person(int age, string name)
    {
        this->age = age;
        strcpy(this->name, name);
    }
    
    ~Person()
    {
    }
    
private:
    void increaseAge()
    {
        age++;
    }
}

Class Inheritance

class Tuple
{
protected:
    int x;
    int y;
    
public:
    Tuple(int i1, int i2)
    {
        x = i1;
        y = i2;
    }

    virtual int sum()
    {
        return i + x;
    }
};

class Triple: public Tuple
{
protected:
    int x;
    int y;
    int z;
    
public:
    Triple(int i1, int i2, i3): Tuple(i1, i2)
    {
        z = i3;
    }

    int sum()
    {
        return x + y + z;
    }
};

"Abstract" Classes

class Animal
{
public:
    virtual void speak()=0;
}


class Cat: public Animal
{
public:
    void speak()
    {
        cout << "Meow" << endl;
    } 
} 

Method Prototypes for Classes

class Cat: public Animal
{
public:
    void speak()
    {
        cout << "Meow" << endl;
    }
    
    int fly(); //method prototype 
} 


// Off in a header file or something
int Cat::fly()
{
    return 42;
}

File IO

Reading From File

#include <fstream>


//in main or somewhere
fstream f;
char c;
f.open("p022_names.txt", ios::in);


while(!f.eof())
{
    f.get(c);
    cout << c;
}
f.close();

Writing to File

#include <fstream>


//in main or somewhere
fstream f;
char c;
f.open("p022_names.txt", ios::out);

f << "stuff in the file " << endl;

int i = 4;

f << i << " this is also in the text file" << endl;

f.close();