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CS1112 Lecture 7 2008/9/
Lecture slides 1
Previous Lecture: Iteration using while
Today’s Lecture: Developing algorithms Nested loops
Announcements: Project 2 due 9/22 (Mon) at 6pm Prelim 1 on 9/25 (Thurs) 7:30pm. If you have a conflict, tell us (email Kelly Patwell) now—no later than tomorrow. You’ll use your clicker for a quiz soon—register it!
Example: Nested Stars
Draw a black square
- Bigger than the biggest star
- Center at (0,0)
- Make side length 2.
Draw a sequence of stars -Stars get smaller -Stars alternate in color -1 st^ star smaller than the sqr -radius r=1 to start -When to stop?
September 18, 2008 Lecture 7 9
Example: Is it prime?
Write a program fragment to determine whether
a given integer n is prime. Assume n>1.
Reminder: rem(x,y) returns the remainder of x
divided by y.
Example: Are they prime?
Given integers a and b, sketch a program that
lists all the prime numbers in the range [a, b].
Assume a,b>1 and a<b.
September 18, 2008 Lecture 7 19
Example: Times Table
Write a script to print a times table for a
specified range.
Row headings
Column headings
CS1112 Lecture 7 2008/9/
Lecture slides 2
Developing the
algorithm for the
times table
disp('Show the times table for a specified range')
lo= input('What is the lower bound? ');
hi= input('What is the upper bound? ');
September 18, 2008 Lecture 7 23
Find the biggest rectangle
Draw 5 rectangles
that the user specifies
using mouse clicks
Color the biggest one
red
Here's the biggest rectangle you drew!
September 18, 2008 Lecture 7 26
Find the mode in a sequence
A mode is the number in a sequence that appears the most number of times Develop an algorithm for calculating the mode of a user- entered sequence that is Non-negative Entered one-by-one in non-decreasing order Terminated by a negative number E.g., sequence 87, 92, 92, 98, 98, 98, 100 has a mode… Write the algorithm and then the code on your own for practice!
September 18, 2008 Lecture 7 28
The savvy programmer…
Learns useful programming patterns and use them where appropriate Seeks inspiration by working through test data “by hand” Asks, “What am I doing?” at each step Declares a variable for each piece of information maintained when working the problem by hand Decomposes the problem into manageable subtasks Refines the solution iteratively, solving simpler subproblems first Remembers to check the problem’s boundary conditions Validates the solution (program) by trying it on test data
