Programming and Problem Solving Software Engineering Read Chap

Programming and Problem Solving — Software Engineering (Read Chap. 2) 1

Problem Solving A Temperature-conversion problem: Write a program that, given a temperature in Celsius, displays that temperature in Fahrenheit. 5 Phases of (Simplified) Software Life Cycle: • Problem Analysis and Specification OCD (Object-Centered Design) • Design • Implementation (Coding) • Testing, Execution and Debugging • Maintenance 2

OCD (Object-Centered Design) 1. Describe the behavior of the program. 2. Identify the problem’s objects and make a table of information about them. 3. Identify the problem’s operations and make a table of information about them. 4. Organize the objects and operations into a sequence of steps, called an algorithm, to solve the problem. 3

Using OCD Behavior A. Describe the desired behavior of the program: Our program should display program information to the user and then a prompt for the Celsius temperature on the screen, read that temperature from the keyboard, compute the corresponding Fahrenheit temperature, and display the result, along with a descriptive label on the screen. 4

Using OCD Problem Objects B. Identify the nouns in the behavioral description (other than "non-behavioral" ones like "program" and "user"): Our program should display program information to the user and then a prompt for the Celsius temperature on the screen, read that temperature from the keyboard, compute the corresponding Fahrenheit temperature, and display that temperature, along with a descriptive label on the screen. These make up the objects in our problem. 5

Using OCD Information about Objects Determine a type and a name (if necessary) for each object and whether it is a constant or a variable. Problem Object Type Kind C++ Type Name program information text constant ? none prompt text constant ? none Celsius temperature real number variable double screen output variable ? cout keyboard input variable ? cin variable double constant ? Fahrenheit temperature real number label text celsius fahrenheit none 6

Using OCD Operations C. Identify the verbs in the behavioral description: Our program should display program information to the user and then a prompt for the Celsius temperature on the screen, read that temperature from the keyboard, compute the corresponding Fahrenheit temperature, and display that temperature, along with a descriptive label on the screen. These make up the operations in our problem. 7

Using OCD Information about Operations Identify the C++ operator to perform a given operation, if there is one. Operation Predefined? C++ Operator Display yes << iostream Read yes >> iostream Compute the Fahrenheit temperature ? ? Library To compute the Fahrenheit temperature, we need to know/find the Celsius to Fahrenheit conversion formula. 8

Using OCD Celsius-to-Fahrenheit Formula for converting Celsius to Fahrenheit: fahrenheit = 1. 8 × celsius + 32 Converting the temperature thus adds new objects and operations to our problem. 9

Using OCD Information about Objects (Revised) Problem Object Type Kind C++ Type Name program information text constant ? none prompt text constant ? none Celsius temperature real number variable double screen output variable ? cout keyboard input variable ? cin variable double constant ? none real number constant double none integer constant int none Fahrenheit temperature real number text label conversion factor 1. 8 conversion factor 32 celsius fahrenheit 10

Using OCD Information about Operations (Revised) Operation Predefined? Display yes << iostream Read yes >> iostream yes * built-in yes + built-in yes = built-in Compute the Fahrenheit temperature: Multiply two real values (1. 8 and celsius) Add a real value (the result above) and an integer (32) Store a real value (the result above) in a variable C++ Operator Library 11

Using OCD Algorithm D. Organize the objects and operations into a sequence of steps that solves the problem, called an algorithm. 1. Display via cout information about the program to the user. 2. Display via cout a prompt for the Celsius temperature. 3. Read the temperature from cin. 4. Compute the Fahrenheit temperature from the Celsius temperature. 5. Display via cout the Fahrenheit temperature and an informative label. 12

Coding Once we have designed an algorithm, the next step is to translate that algorithm into a high level language like C++. This involves writing instructions to — represent the objects, and — perform the operations in C++. 13

/* temperature. cpp converts a Celsius temperature to Fahrenheit. John Doe CS 104 X Lab 1 The Code Jan. 5, 2012 Input: A Celsius temperature Output: Corresponding Fahrenheit temperature ------------------------*/ #include <iostream> using namespace std; // cin, cout, <<, >> int main() { } // 1. Display via cout information about the // program to the user. When learning to program, it is helpful to just start with the algorithm as comments in main() // 2. Display via cout a prompt for the Celsius // temperature. // 3. Read the temperature from cin. // 4. Compute the Fahrenheit temperature from the // Celsius temperature. } // 5. Display via cout the Fahrenheit temperature // and an informative label. 14

/* temperature. cpp converts a Celsius temperature to Fahrenheit. John Doe CS 104 X Lab 1 The Code Jan. 5, 2012 Input: A Celsius temperature Output: Corresponding Fahrenheit temperature ------------------------*/ #include <iostream> using namespace std; // cin, cout, <<, >> int main() { // 1. Display via cout information about the // program to the user. cout << "John Doe CS 104 X -- Lab 1nn"; cout << "** Convert Celsius temps to Fahrenheit **n"; // 2. Display via cout a prompt for the Celsius // temperature. cout << "Please enter a temperature in Celsius: "; 15

The Code // 3. Read the temperature from cin. double celsius; cin >> celsius; // 4. Compute the Fahrenheit temperature from the // Celsius temperature. double fahrenheit = 1. 8 * celsius + 32; } // 5. Display via cout the Fahrenheit temperature // and an informative label. cout << celsius << " degrees Celsius is " << fahrenheit << " degrees Fahrenheit. n"; It’s wise to echo input data to insure computer read what you intended. 16

/* temperature. cpp converts a Celsius temperature to Fahrenheit. John Doe CS 104 X Lab 1 Comments Jan. 5, 2012 Input: A Celsius temperature Output: Corresponding Fahrenheit temperature ------------------------*/ #include <iostream> using namespace std; // cin, cout, <<, >> Always begin a program with int main() opening { documentation // 1. Display via cout information about the enclosed in // program to the user. /* and */. cout << "John Doe CS 104 X -- Lab 1nn"; cout << "** Convert Celsius temps to Fahrenheit **n"; // 2. Display via cout a prompt for the Celsius // temperature. cout << "Please enter a temperature in Celsius: "; 17

/* temperature. cpp converts a Celsius temperature to Fahrenheit. John Doe CS 104 X Lab 1 Jan. 5, 2012 Input: A Celsius temperature Output: Corresponding Fahrenheit temperature ------------------------*/ #include <iostream> using namespace std; // cin, cout, <<, >> int main() { // 1. Display via cout information about the Libraries // program to the user. loads the C++ cout << "John Doe CS 104 X -- Lab This 1nn"; that we need. cout << "** Convert Celsius temps library to Fahrenheit **n"; & Proj. #include <cmath> // 2. Display via cout a prompt. Lab for the 1: Celsius // temperature. cout << "Please enter a temperature in Celsius: "; 18

/* temperature. cpp converts a Celsius temperature to Fahrenheit. John Doe CS 104 X Lab 1 Jan. 5, 2012 Each step of the Input: A Celsius temperature algorithm is implemented Output: Corresponding Fahrenheit temperature by one or more C++ ------------------------*/ program statements #include <iostream> // cin, cout, <<, >> inside main() function. using namespace std; int main() { // 1. Display via cout information about the // program to the user. cout << "John Doe CS 104 X -- Lab 1nn"; cout << "** Convert Celsius temps to Fahrenheit **n"; // 2. Display via cout a prompt for the Celsius Why no n ? // temperature. cout << "Please enter a temperature in Celsius: "; 19

Each step of the algorithm is implemented by one or more C++ program statements // 3. Read the temperature from cin. inside main() function. double celsius; cin >> celsius; // 4. Compute the Fahrenheit temperature from the // Celsius temperature. double fahrenheit = 1. 8 * celsius + 32; // 5. Display via cout the Fahrenheit temperature // and an informative label. Always a good cout << celsius << " degrees Celsius is " idea to << fahrenheit << " degrees Fahrenheit. n"; echo input data } Note spacing, indentation, & alignment to make program “look nice” and easier to read. This will be one criterion used in grading. 20

Testing Run your program using sample data (whose correctness is easy to check): John Doe CS 104 X -- Lab 1 ** Convert Celsius temps to Fahrenheit ** Please enter the temperature in Celsius: 0 0 degrees Celsius is 32 degrees Fahrenheit. John Doe CS 104 X -- Lab 1 ** Convert Celsius temps to Fahrenheit ** Please enter the temperature in Celsius: 100 degrees Celsius is 212 degrees Fahrenheit. 21

When you are convinced that the program is correct, run it with the required data values. John Doe CS 104 X -- Lab 1 ** Convert Celsius temps to Fahrenheit ** Please enter the temperature in Celsius: -17. 78 degrees Celsius is -0. 004 degrees Fahrenheit. 22

Why Testing is Important: For a programming assignment: Lose a few points or may be lucky and the grader doesn’t catch it. For a real-world problem: Much more may be at stake: money, jobs, and even lives. • • September, 1999: Mars Climate Orbiter June, 1996: Ariane 5 rocket March, 1991: DSC Communications February 25, 1991(Gulf War): Patriot missile See Other Course Information (CS 104 page): • Importance of Program Testing — Horror Stories Testing is never finished; it is only stopped. Testing can only show the presence of errors, not their absence. 23

Maintenance • Large % of computer center budgets • Large % of programmer's time • Largest % of software development cost Why? See Other Course Information (CS 104 page): • Time Spent on Program Maintenance Poor structure, poor documentation, poor style ⇒ less likely to catch bugs before release ⇒ fixing of bugs difficult and time-consuming ⇒ impede implementation of enhancements 24