C++ Seed generation

This is a quick tutorial on how to generate pseudo-random seeds in C++. It is important to understand that, this is a two-step process: first - setting a range with ran()%10- this will produce numbers from 0 to 9 (); and second - generating a seed for the program to work with, using srand(123)- this will generate a seed based on those numbers. In this tutorial I will go over 3 examples to demonstrate different outcomes.

The code below will output the same 10 numbers every time the program is ran.

#include "stdafx.h" // - Visual Studio only
#include <stdlib.h>
#include <iostream>

using namespace std;

void genRanNum() {
 int num = 10;
 do {
  cout << rand() % 10 << endl;
  num--;
 } while (num>0);
} 

 

int main()
{

 genRanNum();//--produce 10 random numbers
 cin.get();//-- pause
 
    return 0;

}

To generate a seed that will be different to the default output but same every time it is used, use srand(23232) - with numbers of your choice.

#include "stdafx.h" // - Visual Studio only
#include <stdlib.h>
#include <iostream>

using namespace std;

void genRanNum() {
 int num = 10;
 do {
  cout << rand() % 10 << endl;
  num--;
 } while (num>0);
}

void seedGen(int seed=0) {
 srand(seed);
}
int main()
{
 seedGen(3245);//--generate a seed based on numbers

 genRanNum();//--produce 10 random numbers
 cin.get();//-- pause
 
    return 0;

}

And finally to produce a pseudo-random seed every time the program is used, parse current time value into the srand(time(0)) function as a parameter. Include <time.h> header to work with time.
 

#include "stdafx.h" // - Visual Studio only
#include <stdlib.h>
#include <iostream>
#include <time.h>

using namespace std;

void genRanNum() {
 int num = 10;
 do {
  cout << rand() % 10 << endl;
  num--;
 } while (num>0);
}


void randSeedGen() {
 srand(time(0));
}

int main()
{
 randSeedGen();//--generate a random seed based on time
 
 genRanNum();//--produce random 10 number
 cin.get();//-- pause
 
    return 0;

}

C++ Operator Overloading

C++ compiler can use operators on basic types such as int, float and string. When you create a custom class and try to use an operator, the compiler does not know how to deal with provided information. Here is where operator overloading comes in. C++ allows operator overloading for specific types - effectively you can define custom behaviors for a wide range of operators.

In this example, I use a custom Point class which has x and y values. Shown operators (+,-,*,/,>,<,>>,<<) are altered to exhibit a particular behavior as to compare those values.

//overloading operators

#include "stdafx.h" //-- for Visual Studio only
#include <iostream>
#include <string>

using namespace std;

class Point {

 int _x, _y;

public:
 Point(int x, int y) :
  _x(x), _y(y) {
 }

 int x() const {
  return _x;
 }

 int y() const {
  return _y;
 }
 
 bool operator > (const Point &p)const {
  return (_x + _y) > (p._y + p._y);
 }

 bool operator < (const Point &p)const {
  return (_x + _y) < (p._x + p._y);
 }

 bool operator == (const Point &p)const {
  return (_x == p._x) && ( _x == p._y);
 }

 friend ostream& operator << (ostream& os,const Point &p) {
  os << "(" << p._x << "," << p._y << ")";
  return (os);
 }
 
 friend istream& operator >> (istream &input, Point &p)
 {
  input >> p._x;
  input >> p._y;
  return input;
 }

 Point operator = (Point &p) {
  _x=p._x;
  _y=p._y;
  return *this;  
 }

 Point operator + (const Point &p) const {
  return Point(_x+p._x, _y+p._y);
 }

 Point operator - (const Point &p)const {
  return Point(_x-p._x, _y-p._y);
 }

 Point operator * (const Point &p)const {
  return Point(_x * p._x, _y * p._y);
 }

 Point operator / (const Point &p)const {
  //---check for denominator - 0
  if (p._y == 0)return Point(0, 0);
  return Point(_x / p._x, _y / p._y);
 }
};

int main()
{

 Point alpha(2,2), beta(4,4), gamma(8,8);
 cout << "3 points (custom class)" << endl;
 cout << endl;
 cout << alpha << " alpha" << endl;
 cout << beta << " beta" << endl;
 cout << gamma << " gamma" << endl;
 cout << endl;
 cout << "overloaded operators (+,-,*,/,>,<,>>,<<)" << endl;
 cout << endl;
 cout << (alpha + beta) << " alpha + beta" << endl;
 cout << (alpha + beta + gamma) << " alpha + beta + gamma" << endl;
 cout << (alpha - beta) << " alpha - beta" << endl;
 cout << (alpha * beta) << " alpha * beta" << endl;
 cout << (beta / alpha) << " alpha / beta" << endl;
 cout << (alpha > beta) << "  is alpha bigger than beta (0=false)" << endl;
 cout << (alpha < beta) << "  is alpha smaller than beta (1=true)" << endl;
 cout << endl;
 cout << "3 Points (unaltered after using operators)" << endl;
 cout << endl;
 cout << alpha << " alpha" << endl;
 cout << beta << " beta" << endl;
 cout << gamma << " gamma" << endl;

 cin.get();

    return 0;
}

C++ Exception Handling

This code requires <stdexcept> header. ( alternatively you can prepend namespace “exception::” )

The following code has a simple divide function and some code handling exceptions.
This program would output:
3
error!

The divide function can throw an exception if the denominator is equal to 0. Notice how after dealing with the exception, the compiler breaks out of the code block and does not calculate the third statement.

#include "stdafx.h"// -- only for Visual Studio ( Windows)
#include <iostream>
#include <stdlib.h>
#include <stdexcept>

using namespace std;



int divide(int a, int b) {

 if (b == 0) {
  throw exception();
 }
 return (a / b);

}


int main()
{

 try {
  cout << divide(6, 2) << endl;
  cout << divide(5, 0) << endl;
  cout << divide(5, 5) << endl;
 }
 catch (...){
  cout << "error!" << endl;
 }


 system("pause");// -- only for Visual Studio ( Windows)
    return 0;
}

If you expect a particular exception, you can throw the exception value, and catch it, as shown below.

This code would output:

3

error! 0- cannot be used!

#include "stdafx.h"// -- only for Visual Studio ( Windows)
#include <iostream>
#include <stdlib.h>
#include <stdexcept>

using namespace std;



int divide(int a, int b) {

 if (b == 0) {
  throw b;
 }
 return (a / b);

}


int main()
{

 try {
  cout << divide(6, 2) << endl;
  cout << divide(5, 0) << endl;
  cout << divide(5, 5) << endl;
 }
 catch (int e){
  cout << "error! " << e << "- cannot be used!"<< endl;
 }
 

 system("pause");// -- only for Visual Studio ( Windows)
    return 0;
}