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Previous Lecture: Iteration using while
Today’s Lecture: Nested loops Developing algorithms
Announcements: Due to Feb Break, there’ll be no discussion on Tues but
discussion on Wednesday will take place in the lab. Attendance is optional but please do the exercise! Attend any section on Wednesday to get help. Read Insight §3.2 before discussion next week.
Project 2 due Mon 2/24 at 11pm We do not use break in this course Make use of Piazza, office hrs, and consulting hrs
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Lecture 7 3
x = 1;disp(x)y = x;while y==x && x<=4 && y<=4
x = 2*x;disp(x)
end
What is the last line of output?
A: 1 B: 2 C: 4 D: 8
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Lecture 6 7
Draw a black square;
then draw a magenta disk;
then draw a yellow star.
Review loops/conditionals using user-defined graphics function
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Lecture 6 8
−2 −1 0 1 2 3 4 5 6−3
−2
−1
0
1
2
DrawRect(-1,-2,6,3,’y’)
x and y coordinatesof lower left corner width height
color
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Lecture 6 9
DrawDisk(1,3,4,’r’)
−4 −2 0 2 4 6−2
−1
0
1
2
3
4
5
6
7
8
x and y coordinatesof the center radius
color
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Lecture 6 10
DrawStar(1,3,4,’g’)
−4 −2 0 2 4 6−2
−1
0
1
2
3
4
5
6
7
8
x and y coordinatesof the center “radius”
color
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Lecture 6 11
Color Options
White ‘w’Black ‘k’Red ‘r’Blue ‘b’Green ‘g’Yellow ‘y’Magenta ‘m’Cyan ‘c’
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Lecture 6 12
A simple 3-line script
DrawRect(...)DrawDisk(...)DrawStar(...)
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% drawDemoclose allfigureaxis equal offhold on
DrawRect(0,0,2,2,'k')DrawDisk(1,1,1,'m')DrawStar(1,1,1,'y')
hold off
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Lecture 6 14
% drawDemoclose allfigureaxis equal offhold on
Code fragment to draw the objects (rectangle, disk, star)
hold off
A general graphics framework
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Lecture 7 15
Example: Nested Stars
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Lecture 6 16
Example: Nested Stars
Draw a black square-Bigger than the biggest star (at least 2 times radius of star)- Center at (0,0)
Draw a sequence of stars-Stars alternate in color-Stars get smaller
- radius r=1 to start-1st star smaller than the sqr-When to stop?
- when r is smallnestedStars.m
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Lecture 7 17
Knowing how to draw
How difficult is it to draw
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Lecture 7 18
Pattern for doing something n times
n= _____for k= 1:n
% code to do% that something
end
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Lecture 7 19
x= 0; y= 0; % figure centered at (0,0)
s= 2.1; % side length of squareDrawRect(x-s/2,y-s/2,s,s,’k’)
r= 1; k= 1;while r > 0.1 %r still big
% draw a starif rem(k,2)==1 %odd number
DrawStar(x,y,r,’m’) %magentaelse
DrawStar(x,y,r,’y’) %yellowend% reduce rr= r/1.2;k= k + 1;
end
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Lecture 7 20
x= c; y= c; % figure centered at (c,c)
s= 2.1; % side length of squareDrawRect(x-s/2,y-s/2,s,s,’k’)
r= 1; k= 1;while r > 0.1 %r still big
% draw a starif rem(k,2)==1 %odd number
DrawStar(x,y,r,’m’) %magentaelse
DrawStar(x,y,r,’y’) %yellowend% reduce rr= r/1.2;k= k + 1;
end
for c = 0:2:8
end
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Lecture 7 21
Pattern for doing something n times
n= _____for k= 1:n
% code to do% that something
end
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Lecture 7 22
Example: Are they prime?
Given integers a and b, write a program that lists all the prime numbers in the range [a, b].
Assume a>1, b>1 and a<b.
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Lecture 7 23
Example: Are they prime?Subproblem: Is it prime?
Given integers a and b, write a program that lists all the prime numbers in the range [a, b].
Assume a>1, b>1 and a<b. Write a program fragment to determine whether
a given integer n is prime, n>1. Reminder: rem(x,y) returns the remainder of x
divided by y.
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Lecture 7 24
Example: Are they prime?Subproblem: Is it prime?
Given integers a and b, write a program that lists all the prime numbers in the range [a, b].
Assume a>1, b>1 and a<b. Write a program fragment to determine whether
a given integer n is prime, n>1. Reminder: rem(x,y) returns the remainder of x
divided by y.
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Lecture 7 30
%Given n, display whether it is primedivisor= 2;while ( rem(n,divisor)~=0 )
divisor= divisor + 1;endif (divisor==n)
fprintf(‘%d is prime\n’, n)else
fprintf(‘%d is composite\n’, n)end
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Lecture 7 31
%Given n, display whether it is primedivisor= 2;while ( rem(n,divisor)~=0 )
divisor= divisor + 1;endif (divisor==n)
fprintf(‘%d is prime\n’, n)else
fprintf(‘%d is composite\n’, n)end
for n = a:b
end
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Lecture 7 32
Example: Times Table
9 12 15 18 21
12 16 20 24 28
15 20 25 30 35
18 24 30 36 42
21 28 35 42 49
Write a script to print a times table for a specified range.
3 4 5 6 7
34567
Row headings
Column headings
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Developing the algorithm for the times table
9 12 15 18 21
12 16 20 24 28
15 20 25 30 35
18 24 30 36 42
21 28 35 42 49
3 4 5 6 734567
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Lecture 7 34
Developing the algorithm for the times table
Look for patterns Each entry is row# col# Row#, col# increase regularly
Loop!!! What kind of loop?
for-loop—since the range of the headings will be specified and increment regularly
for each row#, get the products with all the col#s. Then go to next row# and get products with all col#s, …
Nested loops! Details: what will be the print
format? Don’t forget to start new lines. Also need initial input to specify the range.
9 12 15 18 21
12 16 20 24 28
15 20 25 30 35
18 24 30 36 42
21 28 35 42 49
3 4 5 6 734567
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disp('Show the times table for specified range')lo= input('What is the lower bound? ');hi= input('What is the upper bound? ');
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Lecture 7 36
Rational approximation of = 3.141592653589793… Can be closely approximated by fractions,
e.g., 22/7 Rational number: a quotient of two integers Approximate as p/q where p and q are positive
integers ≤M Start with a straight forward solution:
Get M from user Calculate quotient p/q for all combinations of p and q Pick best quotient smallest error