EGR 115 Introduction to Computing for Engineers Branching & Program Design – Part 4 Monday 06 Oct 2014 EGR 115 Introduction to Computing for Engineers

Lecture Outline Monday 06 Oct 2014 EGR 115 Introduction to Computing for Engineers More Branching More Debugging Slide 2 of 16

Branching & Program Design Branching – The Switch Statement Monday 06 Oct 2014 EGR 115 Introduction to Computing for Engineers The “switch” statement is another branching construct  Typically used to test if an expression is equal to one of an enumerated set of choices.  General form of the structure: Slide 3 of 16 switch variable case {value1, …, valueL} some code; case {valueM, …,valueN} some more code;  otherwise even more code; end switch variable case {value1, …, valueL} some code; case {valueM, …,valueN} some more code;  otherwise even more code; end variable = value1, value2, …, or valueN } Code Block #1 } Code Block #2 

Branching & Program Design Branching – The Switch Statement Monday 06 Oct 2014 EGR 115 Introduction to Computing for Engineers An Example:  Output the number of days in a user selected month (NOT a leap year): o Month = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 o Months with 30 days = 9, 4, 6, or 11 o Months with 31 days = 1, 3, 5, 7, 8, 10, or 12 o Months with 28 days = 2 Slide 4 of 16 switch month case {2} disp('This month has 28 days'); case {9, 4, 6, 11} disp('This month has 30 days'); case {1, 3, 5, 7, 8, 10, 12} disp('This month has 31 days'); otherwise disp('Invalid Month'); end GOOD PRACTICE: include otherwise statement to trap illegal values of variable NOTE: Only one case will ever be executed

Branching & Program Design Branching – The Switch Statement Monday 06 Oct 2014 EGR 115 Introduction to Computing for Engineers Comparison between if and switch:  Switch better for enumerated variable  If better for testing variables over continuous ranges Slide 5 of 16 switch month case {2} disp('This month has 28 days'); case {9, 4, 6, 11} disp('This month has 30 days'); case {1, 3, 5, 7, 8, 10, 12} disp('This month has 31 days'); otherwise disp('Invalid Month'); end Code continues on next line if month == 2 disp('This month has 28 days'); elseif (month == 9 | month == 4 |... month == 6 | month == 11) disp('This month has 30 days'); elseif (month == 1 | month == 3 |... month == 5 | month == 7 |... month == 8 | month == 10|... month == 12) disp('This month has 31 days'); else disp('Invalid Month'); end

Branching & Program Design Branching – The Switch Statement Monday 06 Oct 2014 EGR 115 Introduction to Computing for Engineers In Class Programming Exercise:  Prompt the user for an integer from 1 to 10  Respond by telling the user whether it is odd or even number. 1. If your last name begins with A to L (inclusive)  Use the switch construct 2. If your last name begins with M to Z (inclusive)  Use the if construct Slide 6 of 16

Branching & Program Design Branching – The Try/Catch Construct Monday 06 Oct 2014 EGR 115 Introduction to Computing for Engineers Typically, when MATLAB encounters a run-time error in your code the program aborts The Try/Catch construct allows you to “trap” the error and continue with execution Slide 7 of 16 try some statements; catch other statements; end } tries to execute these statements } execute these if an error above

Branching & Program Design Branching – The Try/Catch Construct Monday 06 Oct 2014 EGR 115 Introduction to Computing for Engineers An Example:  Given a row vector a with 10-elements display a(index) Slide 8 of 16 a = [ ]; % A row vector with 10-elements try% Request an index and display a(index) index = input('Which element would you like to display? '); disp(['a(',num2str(index),') = ', num2str(a(index))]); catch% Run this code if an error occurs above disp('Indexing type Run-Time Error: 1 <= index <= 10 '); disp([' You entered index = ', num2str(index)]) end Try_catch_example.m

Branching & Program Design More on Debugging Monday 06 Oct 2014 EGR 115 Introduction to Computing for Engineers More on Debugging:  Debug the program: o There are ~ 6 different errors Slide 9 of 16 more_debugging_w_errors.m

Syntax Error: Should be ‘ input ’ NOT ‘ Input ’ Syntax Error: Should be ‘ input ’ NOT ‘ Input ’ Branching & Program Design Branching – The Switch Statement Monday 06 Oct 2014 EGR 115 Introduction to Computing for Engineers Slide 10 of 16 … % Enter the real coefficients of a quadratic polynomial disp('Enter the coeffs of the quadratic: a x^2 + b x + c') a = Input('Enter the coeff. of x^2 term: a = '); b = Input('Enter the coeff. of x^1 term: b = '); c = Input('Enter the coeff. of x^0 term: c = '); % Compute the Discriminant: Delta = b^2 - 4ac Delta = b^2 - 4*a*c … Syntax Error: Missing a semicolon ‘;’ Syntax Error: Missing a semicolon ‘;’ ; ;

Arithmetic Run-Time Error: Should be ‘/ (2*a) ’ NOT ‘ /0*a ’ Arithmetic Run-Time Error: Should be ‘/ (2*a) ’ NOT ‘ /0*a ’ Logic Error: Should be ‘ x2 ’ NOT ‘ x1 ’ Logic Error: Should be ‘ x2 ’ NOT ‘ x1 ’ Logic Error: Should be ‘ > ’ NOT ‘ < ’ Logic Error: Should be ‘ > ’ NOT ‘ < ’ Branching & Program Design Branching – The Switch Statement Monday 06 Oct 2014 EGR 115 Introduction to Computing for Engineers Slide 11 of 16 … % Solve for the roots of the quadratic polynomial if Delta < 0 % Case of real and distinct roots x1 = (-b + sqrt(Delta)) / 0*a; x2 = (-b - sqrt(Delta)) / 0*a; fprintf(' Real and distinct roots: x1 = %4.2f x2 = %4.2f\n', x1, x2) elseif Delta == 0 % Case of real repeated roots x1 = -b / (2*a); x2 = x1; fprintf(' Real and repeated roots: x1 = %4.2f x2 = %4.2f\n', x1, x2) else % Case of complex roots x1 = (-b + sqrt(Delta)) / (2*a); x2 = (-b - sqrt(Delta)) / (2*a); fprintf(' Imag roots: x1 = %g + j%g and x2 = %g + j%g \n',... real(x1), imag(x1), real(x1), imag(x1)); end …

Assignment Run-Time Error: Should be ‘ num2str(x2) ’ NOT ‘ (x2) ’ Assignment Run-Time Error: Should be ‘ num2str(x2) ’ NOT ‘ (x2) ’ Branching & Program Design Branching – The Switch Statement Monday 06 Oct 2014 EGR 115 Introduction to Computing for Engineers Slide 12 of 16 … % Plot the two roots plot(real(x1), imag(x1),'rx', real(x2), imag(x2),'bo', 'MarkerSize',16, 'LineWidth',5) title(['Roots of polynomial: f(x) = ', poly, ' = 0'], 'FontSize', 16) xlabel('Real Axis'); ylabel('Imag Axis') legend(['x_1=',num2str(x1)],['x_2=', (x2)]) grid

Next Lecture Monday 06 Oct 2014 EGR 115 Introduction to Computing for Engineers An Application Example Slide 13 of 16