General Computer Science for Engineers CISC 106 Lecture 13 - Midterm Review James Atlas Computer and Information Sciences 10/02/2009

Important Notes on Exam Write code Study labs Study Midterm review

Unix Commands When you log into a UNIX terminal ◦ You are in your home directory. ◦ To see the files in your directory.  ls ◦ To make an new folder/directory.  mkdir exampledir ◦ To change directories.  cd exampledir ◦ To go back one directory.  cd.. ◦ To go back to your home directory.  cd

Basic if statements IF statements allow program to make choices whether a condition is met or not if (expression1) statements1; end if (expression2) statements2; end

IF/Elseif Statements if (expression1) statements1; elseif (expression2) statements2; else statements3; end

Major Relational Operators ◦ A < B A is less than B ◦ A > B A is greater than B ◦ A <= B A is less than or equal to B ◦ A >= B A is greater than or equal to B ◦ A == B A is equal to B ◦ A ~= B A not equal B

If statements print “blue” if N <= 5 print “red” if N > 5 and N <= 10 print “green” if N > 10

If statements (cont’d) if (N <= 5) fprintf('blue\n‘); elseif (N > 5 & N <= 10) fprintf('red\n‘); elseif (N > 10) fprintf('green\n‘); end

Switch construct color = ‘yellow’; switch (color) case ‘red’ disp(‘Stop now!’); case ‘green’ disp(‘Proceed through intersection.’); case ‘yellow’ disp(‘Prepare to stop.’); otherwise disp(‘Illegal color encountered.’); end

Logical Operators &, && - AND |, || - OR ~ - NOT

Logical Operators Evaluate the following as true or false for x=5:  x < 7 & 3 < x 2. ˜ (x / 2 > 1 & x < 0)  x ˜ = 5 & x + 2 > 6 | x > 5  x + x == 2 * x && ˜ x

Functions.m-file ◦ Function name same as file name Contains a function name, arguments, output, and “implementation” ◦ Contract ◦ Description ◦ Examples All variables in function are local ◦ They are not visible outside call!

Example Function %circleArea(number) -> number %Authors: James Atlas %CISC106 Lab Section 45 TA: Scott Ivanka %Description: % This function computes the area of a circle given the radius. %Examples: % circleArea(3) -> 28 % circleArea(5) -> 78 % circleArea(45) -> 6362 function output = circleArea(radius) output = pi * radius * radius;

Recursive Function Function that refers to itself Example: sum numbers 1 to n function out=sum(n) if n < 1 out = 0; else out = n + sum(n - 1);

Recursive Function Function that refers to itself Example: sum numbers 1 to n function out=sum(n) if n < 1 out = 0; else out = n + sum(n - 1);

Tracing Functions Non-recursive, call to function a() function out = a() out = b(); function out = b() out = c(); function out = c() out = 5;

Tracing Functions functionarglocal return value function out = a() out = b(); function out = b() out = c(); function out = c() out = 5;

Tracing Functions ab() functionarglocalreturn value function out = a() out = b(); function out = b() out = c(); function out = c() out = 5;

Tracing Functions ab() bc() functionarglocalreturn value function out = a() out = b(); function out = b() out = c(); function out = c() out = 5;

Tracing Functions ab() bc() c 5 functionarglocalreturn value function out = a() out = b(); function out = b() out = c(); function out = c() out = 5;

Tracing Functions ab() b5 5 c 5 functionarglocalreturn value function out = a() out = b(); function out = b() out = c(); function out = c() out = 5;

Tracing Functions a5 5 b5 5 c 5 functionarglocalreturn value function out = a() out = b(); function out = b() out = c(); function out = c() out = 5;

Tracing Functions a5 5 b5 5 c 5 functionarglocalreturn value function out = a() out = b(); function out = b() out = c(); function out = c() out = 5;

Tracing Recursion Recursive call to function sum(3) function out=sum(n) if n < 1 out = 0; else out = n + sum(n - 1);

Tracing Recursion sum(n) if n < 1 out = 0; else out = n + sum(n - 1); sumn=3sum(2) functionarglocalreturn value

Tracing Recursion sum(n) if n < 1 out = 0; else out = n + sum(n - 1); sumn=3sum(2) functionarglocalreturn value sumn=2sum(1)

Tracing Recursion sum(n) if n < 1 out = 0; else out = n + sum(n - 1); sumn=3sum(2) functionarglocalreturn value sumn=2sum(1) sumn=1sum(0)

Tracing Recursion sum(n) if n < 1 out = 0; else out = n + sum(n - 1); sumn=3sum(2) functionarglocalreturn value sumn=2sum(1) sumn=1sum(0) sumn=0 0

Tracing Recursion sum(n) if n < 1 out = 0; else out = n + sum(n - 1); sumn=3sum(2) functionarglocalreturn value sumn=2sum(1) sumn=10 1 sumn=0 0

Tracing Recursion sum(n) if n < 1 out = 0; else out = n + sum(n - 1); sumn=3sum(2) functionarglocalreturn value sumn=21 3 sumn=10 1 sumn=0 0

Tracing Recursion sum(n) if n < 1 out = 0; else out = n + sum(n - 1); sumn=33 6 functionarglocalreturn value sumn=21 3 sumn=10 1 sumn=0 0

Tracing Recursion sum(n) if n < 1 out = 0; else out = n + sum(n - 1); sumn=33 6 functionarglocalreturn value sumn=21 3 sumn=10 1 sumn=0 0

Arrays All variables in matlab are arrays An array of one element is called a scalar A one dimension array is called a vector x=3.14;  scalar a = [1,2,3,4,5];  vector

Arrays Interval notation x = 1:0.5:5 Now x is a vector of numbers: x = [1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0]

Arrays (aka matrices) A = [1, 2; 3, 4; 5, 6] Creates a 3x2 matrix, 3 rows, 2 columns. semicolon creates a new row. A =

a = [ ] b = [1; 2; 3; 4] c = [1 2; 3] (error) d = [1 2; 3 4] f = d(1,2) g(4,5) = 7 a(3:end) a(1:2:end) d’ Array commands

For Loops Used when you know how many times code is to be executed. Syntax for = : : Variable is initially the start value At end of iteration variable changes by increment If value is not greater than end the loop runs again.

Example Problem total = 0; for i = 1:1:1000 loop starts at 1 total = total + i;loop increments by 1 end loop ends at 1000 disp(total);

A Loop Analogy (for) The runner executes a loop. If they know the distance they want to run For loop for lapCount = start : 1 : end runLap() end

A Loop Analogy (while) The runner executes a loop. If they don’t know the distance they want to run (run until tired) While loop tired = false; while(~tired) tired = runLap() end