COMPUTAÇÃO E PROGRAMAÇÃO

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1 COMPUTAÇÃO E PROGRAMAÇÃO 1º Semestre 2015/2016 MEMec, LEAN Ficha da Aula Prática 2: Entrada/saída de dados. Scripts. Estruturas de selecção. Sumário das tarefas e objectivos da aula: 1. Utilizar funções de entrada/saída 2. Criar e utilizar scripts 3. Criar gráficos simples 4. Implementar expressões relacionais 5. Utilizar estruturas de selecção NOTA 1: Durante a resolução dos exercícios deverá consultar as apresentações das aulas teóricas, e/ou o livro de apoio da disciplina. NOTA 2: antes de começar cada aula deve-se mudar a directoria de trabalho para uma directoria na pen-drive do aluno, isto garante que o aluno ficará com todos os ficheiros que sejam eventualmente criados durante a aula. NOTA 3: Para facilitar o seu estudo autónomo, os exercícios que não são aplicáveis ao FreeMat são indicados com a letra M após o número. Todos os restantes podem ser resolvidos em qualquer dos programas. Note que as funções (incluindo o comando help) podem não ter exactamente a mesma forma de utilização num e noutro. Consulte a ajuda dos programas através da barra de menus para esclarecer estes casos. Exercícios a resolver na aula Docente Alunos (recomados) Alunos 2.8, 2.19, , 2.3, 3.14, 3.22 Challenge Computação e Programação, LEAN, MEMec 1

2 1. Exemplo de Script Utilize o editor do Matlab para criar o seguinte script: Guarde o ficheiro com o nome script_rectangulo.m e em seguida teste o script na Command Window conforme o exemplo seguinte (a azul as entradas do utilizador): >> script_rectangulo Lado 1 = Lado 2 = 3.1 Área = Perímetro = Apague as variáveis do ambiente de trabalho e carregue o ficheiro rectangulo.mat utilizando a função load. Verifique o valor das variáveis lidas do ficheiro. Note que sempre que executar o script script_rectangulo.m, vai reescrever o conteúdo do ficheiro de dados rectangulo.mat. 2. Funções de Entrada/Saída, Scripts e Gráficos 2. The atomic weight is the weight of an atom of a chemical element. For example, the atomic weight of oxygen is and the atomic weight of hydrogen is Write a script that will calculate the molecular weight of hydrogen peroxide, which consists of two atoms of hydrogen and two atoms of oxygen. Include comments in the script. Use help to view the comment in your script. 3. Write an input statement that will prompt the user for a string. Then, find the length of the string. 4. Write an input statement that will prompt the user for a real number, and store it in a variable. Then, use the fprintf function to print the value of this variable using two decimal places. Computação e Programação, LEAN, MEMec 2

3 5. The input function can be used to enter a vector; for example, >> vec = input('enter a vector:') Enter a vector: 4:7 vec = Experiment with this, and find out how the user can enter a matrix. 7. Experiment, in the Command Window, with using the fprintf function for integers. Make a note of what happens for each. Use fprintf to print the integer without specifying any field width in a field width of 5 in a field width of 8 in a field width of 3 8. Create the following variables: x = 12.34; y = 4.56; Then, write fprintf statements using these variables that will accomplish the following: x is x is 12 x is '12' y is 4.6 y is 4.6! y is 5 % 9. Write a script to prompt the user for the length and width of a rectangle, and print its area with two decimal places. Put comments in the script. 10. Write a script called echoname that will prompt the user for his or her name, and then echo print the name in a sentence in the following format (use %s to print it): >> echoname What is your name? Susan Wow, your name is Susan! 12. Write a script that will prompt the user for an angle in degrees. It will then calculate the angle in radians, and then print the result. Note: radians = Wing loading, which is the airplane weight divided by the wing area, is an important design factor in aeronautical engineering. Write a script that will prompt the user for the weight of the aircraft in kilograms, and the wing area in meters squared, and will calculate and print the wing loading of the aircraft in kg/m Write a script that assigns values for the x-coordinate and then y-coordinate of a point, and then plots this using a green Create a vector x with values ranging from 1 to 100 in steps of 5. Create a vector y that is the square root of each value in x. Plot these points. Now, use the bar function instead of plot to get a bar chart instead. Computação e Programação, LEAN, MEMec 3

4 19. Plot sin (x) for x values ranging from 0 to π (in separate Figure Windows): using 10 points in this range using 100 points in this range 20. Atmospheric properties such as temperature, air density, and air pressure are important in aviation. Create a file that stores temperatures in degrees Kelvin at various altitudes. The altitudes are in the first column and the temperatures in the second. For example, it may look like this: Write a script that uses the function load to read this data into a matrix, then it will separate the matrix into two vectors, and finally plot the data with appropriate axis labels and a title. 34. Write a script called pickone that will prompt the user to input a vector x, and will return one random element from the vector. Write the script so that it can show a help message if needed. For example, >> pickone Please input a vector: [ ] I picked 2! >> help pickone pickone - will prompt the user to input a vector, and then return a random element from it. 3. Scripts, Expressões relacionais e Estruturas de Selecção 4. Write a script to calculate the volume of a pyramid, which is 1/3*base*height, where the base is length*width. Prompt the user to enter values for the length, width, and the height and then calculate the volume of the pyramid. When the user enters each value, he or she will then be prompted also for either i for inches, or c for centimeters. (Note: 2.54cm = 1 inch). The script should print the volume in cubic inches with three decimal places. As an example, the format will be: This program will calculate the volume of a pyramid. Enter the length of the base: 50 Is that i or c? i Enter the width of the base: 6 Is that i or c? c Enter the height: 4 Is that i or c? i The volume of the pyramid is xxx.xxx cubic inches. 7. Write a script that will prompt the user for a numerator and a denominator for a fraction. If the denominator is 0, it will print an error message saying that division by 0 is not possible. If the denominator is not 0, it will print the result of the fraction. Computação e Programação, LEAN, MEMec 4

5 9. The continuity equation in fluid dynamics for steady fluid flow through a stream tube equates the product of the density, velocity, and area at two points that have varying cross-sectional areas. For incompressible flow, the densities are constant so the equation is A 1V 1 = A 2V 2. If the areas and V 1 are known, V 2 can be found as V 1A 1 / A 2. Therefore, whether the velocity at the second point increases or decreases deps on the areas at the two points. Write a script that will prompt the user for the two areas in meters squared, and will print whether the velocity at the second point will increase, decrease, or remain the same as at the first point. 14. Write a script that will prompt the user for a temperature in degrees Celsius, and then an F for Fahrenheit or K for Kelvin. The script will print the corresponding temperature in the scale specified by the user. For example, the output might look like this: Enter the temp in degrees C: 29.3 Do you want F or K? F The temp in degrees F is 84.7 The format of the output should be exactly as specified here. The conversions are: F = 9/5 * C + 32 K = C Write a script that will generate one random integer, and will print whether the random integer is an even or an odd number. Hint: An even number is divisible by 2, whereas an odd number is not, so check the remainder after dividing by Clouds are generally classified as high, middle, or low level. The height of the cloud is the determining factor, but the ranges vary deping on the temperature. For example, in tropical regions the classifications may be based on the following height ranges (given in feet): low middle high > Write a script that will prompt the user for the height of the cloud in feet, and print the classification. 22. Rewrite the following switch statement as one nested if-else statement (elseif clauses may be used). Assume that there is a variable letter and that it has been initialized. switch letter case 'x' disp('hello') case {'y', 'Y'} disp('yes') case 'Q' disp('quit') otherwise disp('error') Computação e Programação, LEAN, MEMec 5

6 24. In a certain city, there are five different trolley lines; they have the codes A, B, C, D, and E. Assume that code is a char variable that has been initialized. The following nested if-else statement prints the frequency with which a given line is supposed to run: if (code > 'A' && code < 'E') if (code == 'C') fprintf('every 10 minutes\n') else fprintf('every 7 minutes\n') else if (code == 'A') fprintf('this line is now obsolete!\n') else if (code = 'E') fprintf('error - there is no such trolley!\n') else fprintf('every 12 minutes\n') This is confusing! Rewrite this as a switch statement that does exactly what the above nested if-else statement does, for any given value of the variable code. Do not use any if or if-else statements (there should only be fprintf statements in the switch). Put this in a script that will test the solution. 25. Write a script area_menu.m that will print a list consisting of cylinder, circle, and rectangle. It prompts the user to choose one, and then prompts the user for the appropriate quantities (e.g., the radius of the circle) and then prints its area. If the user enters an invalid choice, the script simply prints an error message. The script should use a switch statement to accomplish this. Here are two examples of running it. >> area_menu Menu 1. Cylinder 2. Circle 3. Rectangle Please choose one: 2 Enter the radius of the circle: 4.1 The area is >> area_menu Menu 1. Cylinder 2. Circle 3. Rectangle Please choose one: 3 Enter the length: 4 Enter the width: 6 The area is Computação e Programação, LEAN, MEMec 6

7 4. Challenge Nível Exercício 1. What would be the result of the following expressions? (NOTA: tente perceber antes de testar!!!) 'b' >= 'c' == (3 == 2) + 1 xor(5 < 6, 8 > 4) 2.6. Experiment, in the Command Window, with using the fprintf function for real numbers. Make a note of what happens for each. Use fprintf to print the real number without specifying any field width in a field width of 10 with four decimal places in a field width of 10 with two decimal places in a field width of 6 with four decimal places in a field width of 2 with four decimal places Plot exp(x) for values of x ranging from 2 to 2 in steps of 0.1. Put an appropriate title on the plot, and label the axes In a script, the user is supposed to enter either a y or n in response to a prompt. The user s input is read into a character variable called letter. The script will print "OK, continuing" if the user enters either a y or Y or it will print "OK, halting" if the user enters an n or N, or it will print "Error" if the user enters anything else. Put this statement in the script first: letter = input('enter your answer: ', 's'); Write the script using a switch statement Write a script to prompt the user for a character, and then print whether or not it is a letter of the alphabet If the lengths of two sides of a triangle and the angle between them are known, the length of the third side can be calculated. Given the lengths of two sides (b and c) of a triangle, and the angle between them in degrees, the third side a is calculated as: a 2 = b 2 + c 2 2 b c cos(φ) Write a script called thirdside.m that will prompt the user and read in values for b, c, and φ (in degrees, 1 deg = π/180 rad), and then calculate and print the value of a with three decimal places. The format of the output from the script should look exactly like this: >> thirdside Enter the first side: 2.2 Enter the second side: 4.4 Enter the angle between them: 50 The third side is Computação e Programação, LEAN, MEMec 7

8 3 Crie um programa que peça ao utilizador um número inteiro representando um dia, e outro representando um mês do ano, e que para cada um verifique se o valor introduzido faz sentido (1 <= dia <= 31, 1 <= dia <= 30, ou 1 <= dia <= 28 consoante o mês e 1 <= mês <= 12, não se preocupe com os anos bissextos). Se algum dos valores não fizer sentido o programa deve apresentar uma mensagem de erro, caso contrário indica ao utilizador qual o número de dias decorridos nesse ano até à data introduzida. Por exemplo: se o utilizador introduzir 22 para o dia e 5 para o mês o programa indicará que se trata do 142º dia do ano. Referências Capítulos 2 e 3 do livro de apoio: Matlab: A Practical Introduction to Programming and Problem Solving 2nd edition Apresentações das AT 4 e AT 5 Computação e Programação, LEAN, MEMec 8