CSC 306 Introduction to Programming with C++

Pseudorandom Numbers in C++

Chapter 6

Objectives

• Learn more details on using loops
• Introduce the C++ for loop
• Learn to create and use pseudo-random numbers in C++
• Learn new terminology:

Important Definitions

• for loop
• pseudo-random numbers
• random number seed

For Loops

1. Initialization - the counter variable (if one is used) is assigned an initial value.
2. Condition of repeat - A conditional statement (recall they evaluate to either true or false) is used to determine if the loop should repeat or stop.
3. Counter variable update - note that without this step, the result is an infinite loop.

int number;
char character;

number = 32;
while (number <= 126) {
  character = number;
  cout << "The character '" << character;
  cout << "' is represented as the number ";
  cout << number << " in the computer.\n";
  number++;
}

int number;
char character;


for (number = 32 ; number <= 126 ; number++) {
  character = number;
  cout << "The character '" << character;
  cout << "' is represented as the number ";
  cout << number << " in the computer.\n";
}

for( initialization; repetition_condition ; update ) { Statement 1; ... Statement N; }

Note that the update on the counter variable (the statement "number++" in the example above) occurs in the third part within the parentheses of the for loop and as the last statement in the body of the while loop.

Pseudo-random Numbers

For example, suppose that a pseudo-random number generator exists called genRand() that returns double numbers between 0 and one, and it is used in the following function:

	// This function will extract 6 pseudorandom numbers using the genRand() // function. void extractRandomness() { double thisRand; int numberExtracted=0; while( numberExtracted < 6 ) { thisRand = genRand(); numberExtracted++; } }

Running the program once will generate a sequence of numbers, such as "0.45, 0.398, 0.956, 0.562, 0.874, 0.012". Running the program again will generate the same sequence. Having the same sequence generated each time is useful for debugging purposes but not for some applications that rely on truly random numbers, such as games. To generate a different random sequence each time, it is necessary to set a different seed. (Of course, now the seed must be different because otherwise the program starts generating random numbers from the same point) The standard way to set a different seed each time is to use the current clock time because this value changes each time the program runs.

The RollDice.cpp program contains two classes it uses to simulate rolloing dice: (1) a RandGen class that generates pseudo-random numbers and (2) a Dice class. Try running the program several times to see what it does.

Assignment Specifics

You are to use the Dice and RandGen classes given in the RollDice.cpp program defined above to explore pseudo-random numbers on the computer.

• Write program that asks the user how many dice rolls they would like to have and how many sides their dice will have.

• Use a for loop in your main program to roll the specified die the given number of times, outputing to the console the result of each of the rolls.

• At the end of the loop, print out the average dice roll, the high dice roll, and the low dice roll.

• Add an error testing function to the dice class so that when a user specifies the number of sides to be less than equal to 0, the dice is set to a six-sided die by default and the user is given a warning.

Be sure to do the following:

• Include comments for any parts of the code that is non-intuitive to let us know what that portion does.

• Use meaningful variable names for functions and have them return values of the appropriate types. i.e. something is not a good name, but calculatesInverse is.

• Test your program with a variety of inputs, such as the same points, and point for which you know the distance

• Include a descriptive header as a comment at the top of your source code as follows:

      // Course: CSC 306 Introduction to Programming with C++ 
      // Name: Your Name
      // Assignment #16: <Put a brief sentence about your program here.>
      /* 
         Purpose: <Put a more in-depth description of the program here.>
       */
  

When you are finished writing and testing your assignment, drop your source code file into the CSC306_A12 dropbox on the Academic server.