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Exercises

  1. In exercise 2 of Lesson 15 you should have developed an algorithm for the following problem:
    A set of numbers is to be entered to the computer and the number of negative and the number of positive values entered are to be output. All the numbers lie between -100.0 and 100.0.
    Now implement your algorithm as a C++ program using a while loop and a sentinel value to terminate input. Make up a suitable small set of data and choose a suitable sentinel value to terminate input and test your program.

  2. In exercise 3 of Lesson 15 you should have developed an algorithm to generate all powers of two up to the largest power less than 10,000. Now implement this as a C++ program. Once you have this working change the program so that the user can enter a value for the stopping value (i.e. a value to replace the 10,000). If you try to enter a value that would cause a number greater than the largest int variable possible to be generated then errors will occur! The form the error will take will depend on the compiler being used, it might generate erroneous results and/or get stuck in an infinite loop. The onset of this problem can be delayed by declaring the integer variables holding the limit and the power of two as being of type long int which will allow these variables to take values up to a 10 digit integer. It is important while programming to remember that there are limitations on the size and precision that numerical values can take, if these limitations are not kept in mind nonsensical results can be produced.

  3. The standard C++ library contains functions to generate random numbers. Consider the following C++ program which will print out ten random integers:
    #include <stdlib.h>
#include <time.h>
#include <iostream.h>

void main()
{
 int r;                   // random integer;
 int i = 0;               // control variable
 srand(time(0));                 // initialise random number generator
 while (i < 10)
   {
    r = rand();           // gets random int in 0-RAND_MAX
    cout << "Random integer was " << r;
    i++;
   }
}
    Note that the function srand is used once at the beginning of main, this ensures that the random number sequence will start at a different value each time that the program is run. If the call of srand was left out then the program would deliver exactly the same results each time it was run, not very random! The function rand() returns a random integer in the range 0 to RAND_MAX. RAND_MAX is a const int defined in the include file stdlib.h. The use of time(0) as an argument to srand ensures that a new starting value is used each time the program is run. Note that the inclusion of the files stdlib.h and time.h is required before these functions can be used.

    Now extend the above program so that it generates n random numbers, where n is entered by the user, and counts how many of the random integers generated are less than a half of RAND_MAX. If the random number generator is producing a uniform spread of random numbers in the interval then this should converge towards a half of n. Execute your program with increasing values of n (but not bigger than 32767).


Next: The do-while statement Up: The while statement Previous: Review Questions