Carnegie Mellon University

Java Programming

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Coin Toss Simulation 1

import java.util.Random; public class CoinToss1 { private static int heads = 0; private static int tails = 0; private static int toss; private static Random rand; public static void main(String args[ ]) { rand = new Random(); for( toss = 1; toss <= 500; toss++) { if ( (rand.nextInt() % 2) == 1 ) heads++; else tails++; } System.out.print(heads + “ heads "); System.out.println(tails + " tails “); } }

Here is a program that simulates the toss of a coin 500 times. From the results shown above, it hardly seems like a “fair” coin.

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Look at the program above. The intent of this program is to simulate 500 tosses of a fair coin.

For the variable heads to increment, the expression ( rand.nextInt() % 2) must return a 1. Can the expression ( rand.nextInt() % 2) return a 1?
Answer. Yes, the expression ( rand.nextInt() % 2) returns a 0 or a 1.

The program simulates a coin tossing experiment. 500 tosses are made. Probability states that a fair coin should come up heads as often as it does tails. But the results shown above do not seem very fair.

If we run the program again, will we get exactly the same results?
No, the results will not be exactly the same because the seed value for the random number algorithm is determined by the time at which the program runs.