1. Computer Science I:
Get out your notes.
Understand how to evaluate expressions with
10 minutes online time to finish program
DIV and MOD
Random Numbers
Reading random code
Writing random code
Odds/evens/…

2. Program options from Last Class
10 minutes to finish up program
Input: 10 ages
Output: The age of the oldest person.
Push: Also enter names and output the name and age of the oldest person
Push: Show the name and age for the top 3.
Push: Calculate the average age
Input: 10 times (in seconds)
Output: The fastest time.
Push: Also enter names and output the name and time of the fastest person
Push: Show the name and time for the top 3.
Push: Calculate the average time
Challenge:
What is 4(1/1 - 1/3 + 1/5-1/7+1/9…)?
Write a program to determine and prove your proposal.

3. Learning Objectives
Review a program that uses a for loop with a dry run.
Review DIV and MOD operations.
Be able to read a program that uses random numbers.
Be able to write a program that uses random numbers.

4. Dry Run the Following

5. DIV = Integer Division 20 DIV 9 10 DIV 3 21 DIV 12 9 DIV 10 5 DIV 2

6. MOD = Remainder of Integer Division

7. Random Numbers…why use them?
Testing data
Modeling
Gaming
Adding ‘chance’ to something

8. How do you do it? Seed the computer’s random number generator
Randomize; {Command}
Make the computer generate a random number in a given range.
Random command
Number:= random(12)+ 2;

9. Syntax Answer:= random(range) + offset;
Coin:= random(2)+1;
Die:= random(6)+1;
Answer:= 2*random(range) + offset;
Evans/Odds
Evento100:= 2*random(50)+2;
Oddto99:=2*random(50)+1

10. Example Program
program flipper; var count, coin:integer; begin randomize; for count := 1 to 50 do coin:= random(2) + 1; {1 = heads, 2 = tails} if coin = 1 then writeln('Heads') else writeln('Tails'); end; {Of the for loop} end. {Of the program}

11. Reading code
Name the range of values that the following could generate
Ans:= random(5);
Ans:= random(6)+2;
Ans:= random(40)-7;
Ans:= 2*random(10)+3;
Ans:= 2*random(9)-7;

12. Writing code
Write the random line to generate a number for the following ranges.
1-6
2-30
A pair of 6-sided dice
3-9 odd
12-24 even

13. Check for Understanding: Find the range of values the following code produces.
1) ans:=random(6)+1;
2) ans:=random(14)+2;
3) ans:=random(7)-4;
4) ans:=random(12)+5;
5) ans:=random(23)+8;
6) ans:=random(50)-5;
7) ans:=random(18)+370;
8) ans:=2* random(10) + 1;
9) ans:=2* random(9) + 6;
10) ans:=2* random(21) + 10;
11) ans:=2* random(100) + 51;

14. Check for Understanding: Write the line of code to generate the following ranges of values
8 to 24 even
7 to 35 odd
-7 to 21 odd
-10 to 10 even
A pair of six sided dice

15. Program options If you are stuck… Hands on, Pseudo-code, Dry run,
Flip a coin 100 times, show the total number of heads and tails AND which occurred the most often.
Roll a pair of 6 sided dice 100 times. Find out which occurs most often, 3 or 11. Show how often each of these rolls occur and which occurs most often.
Math tutor:
User inputs the number of sample addition problems o show.
The computer generates the problems and shows them to the user.
The user guesses the answers
At the end the computer shows how many the user answered correctly.