UMBC CMSC201, Computer Science I, Fall 1994 Sections 0101, 0102 and Honors

Tuesday November 1, 1994

Assigned Reading: 8.2 - 8.5

Handouts (available on-line): none

Topics Covered:

• Discussion on various types of interfaces: between hardware and software, and between operating systems and application software. Buzzwords for the day: "interchangeable parts for software."
• We started developing a library for generating random numbers. Our first program simply called the function rand() to print out many random numbers. One problem with this program is that the output from the program is the same set of random numbers.
• We consulted the manual to solve this problem. First we issued the UNIX command:

  	man -k random
       

  to get a list of functions related to the word "random". Then, we looked at the manual pages for the function rand() by typing:

  	man rand
       

• Using the information from the manual pages, we wrote a second program that sets the random seed by asking the user for a random number. Now, the program gives different output if the user types in a different random seed. However, if the user types in the same seed, the program still generates identical output.
• To fix this second problem, we want to use the system clock to set the random seed. So, we consulted the manual pages for the time function.
• The third version of our program uses the time function to set the random seed. This program prints out a different list of random numbers every time. In order to use the time function properly we needed to include the header file time.h at the beginning of the program. (We knew this from reading the manual.)
• We then wrote the fourth version of the program which prints a list of random numbers between 1 and 6, so we can simulate the roll of a six-sided die.
• Finally, we broke up our program into several functions and used defined constants instead of magic numbers. The output shows the result of calling the GetRandomNumber() function twice to simulate rolling two six-sided dice.