The document discusses how to generate random numbers in C++ for various purposes like games and simulations. It explains that the random() function generates a random integer between 0 and the parameter minus 1. It provides examples of using random numbers to simulate coin tosses, dice rolls, and randomly selecting items from arrays. The randomize() function initializes the random number generator with a new seed value, ensuring different random sequences each time.

1. CBSE, Grade 12
Computer Science
Random Numbers - Notes
Malathi Senthil,
senthil.malathi@gmail.com
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2. 1. Why do we need to generate
random numbers?
 Have you ever played the game “TEMPLE RUN”?
 Hope you noticed that the path run is not the same every
time the game is played.
 Yes, the path is randomly picked up.
 What about the path and coins in the game “SUBWAY
SURFERS”?
 The path and coins are at random as well.
 Other typical examples would be
 Tossing coin in cricket
 Rolling dice in board game

3. 2. How to generate a random
number?
 Header file required – stdlib.h
 Random(n) generates any random number from 0 to n-1
 Example # 1
int r = random(4);
Possible values for r are:
 3
 2
 1
 0
 Example # 2
int r = random(0);
The only possible value for r is zero (0)
 The minimum number generated by random(n) is zero
(0)
 The maximum number generated by random(n) is (n-1)

4. 3. Tossing a coin
 Let us assume that 0 indicates head and 1 indicates tail.
 To simulate the toss of a coin with this assumption, the
following code is required:
#include<iostream.h>
#include<stdlib.h>
#include<conio.h>
#include<stdio.h>
void main()
{
int toss;
toss = random(2);
//Possible values for toss are 0 and 1
if (toss==0)
cout<<“Head”;
else
cout<<“Tail”;
getchar();
}

5. 4. Rolling a dice
 When a dice is rolled, the possible outcomes are
1,2,3,4,5 or 6 at random. Nobody can really predict the
outcome.
 Sample source for rolling a dice is given below (header
files are excluded)
void main()
{
int dice;
dice = random(6)+1;
//Possible values for dice are 1,2,3,4,5 or 6
cout<<“The number rolled is ”<<dice;
getchar();
}
 Random(6) generates number 0,1,2,3,4,5 at random
 1 is added to random(6) such that 0 is not generated
and 1 is the minimum number generated.

6. 5. How to generate 3 consecutive
random numbers?
 Simply have for loop to do the job
void main()
{
int how_many=3, dice;
for(int i=0;i<how_many;i++);
{
dice = random(6)+1;
//Possible values for dice are 1,2,3,4,5 or 6
cout<<“The number rolled is ”<<dice;
}
getchar();
}
 The problem with the above code is that we get the
same sequence of random numbers every time we
execute

7. 6. How to get numbers at
random for every execution?
 Use randomize() function before calling random(6)
 Randomize() function initializes random number generator
with a random value
void main()
{
int how_many=3, dice;
randomize();
for(int i=0;i<how_many;i++);
{
dice = random(6)+1;
//Possible values for dice are 1,2,3,4,5 or 6
cout<<“The number rolled is ”<<dice;
}
getchar();
}

8. 7. How to pick up one of your
favourite geeks at random?
 The example below is a simple one to pick up one of the
3 geeks stored in an array.
void main()
{
char my_geeks[][20]={“Steve Jobs”,”Bill Gates”,”Larry Page”};
int rnd;
randomize();
rnd = random(3);
//Possible values for rnd are 0,1 or 2
cout<<“My favourite geek is ”<<my_geeks[rnd];
//One of the geeks will be picked up at random
getchar();
}

9. 8. How to pick up 2 of my
favourite cricketers at random?
 For loop will rescue us now
void main()
{
char cricketers[][20]={“Dhoni”,”Kohli”};
int rnd_player;
randomize();
for (int i=0;i<2;i++)
{
rnd_player = random(2);
//Possible values for rnd_friend are 0 or 1
cout<<cricketers[rnd_player]<<“#”;
//Same player may be picked up in
//the 2nd iteration
}
getchar();
}
 Possible outcomes are:
 Dhoni#Dhoni#
 Kohli#Kohli#
 Dhoni#Kohli#
 Kohli#Dhoni#

10. 9. Rec@p...
 stdlib.h is the header file required
 random(n) generates a random number between 0 and
n-1
 randomize() function is used to initiate random number
generator with a random value
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