CS161 Introduction to Computer Science

1. CS161 Introduction to Computer Science Topic #2 CS161 Topic #2

2. Today in CS161 • Lecture • Handouts you should have • Solving Problems with Computers • Write a short Algorithm • Assignments • Walk through Program #1 -- step by step • Question Session CS161 Topic #2

3. CS161 Handouts: • From the web site, make sure to look at: (www.cs.pdx.edu/~karlaf) • Syllabus • Course Outline • Style Sheet • C++ Style Requirements • Program Cover Sheet CS161 Topic #2

4. Solving Problems w/ Computers • Programs are... • an expression of a series of instructions that the computer must perform • written in precise languages, called programming languages • Programming languages... • translate your ideas into specific language that the computer will understand • C, C++, Java, Pascal, Visual Basic, Cobol, Fortran CS161 Topic #2

5. Solving Problems w/ Computers • The most difficult part of programming is figuring out how to design a method to solve a problem • Only then do we translate this into C++! • Therefore, start by writing an algorithm once you understand the problem CS161 Topic #2

6. Solving Problems w/ Computers • An algorithm is a sequence of step by step instructions for performing some task -- usually for computation • An algorithm must... • accomplish the task • be clear and easy to understand • define the sequence of steps needed to accomplish the task in the order specified CS161 Topic #2

7. Algorithms • It is best to ignore the details of your programming language (C++) when trying to solve a problem • Instead, figure out the steps you need to go thru to solve the problem • Write these steps down in English • These steps are called the algorithm! CS161 Topic #2

8. Algorithms • Think of your algorithm as a tool for creating the instructions for solving a problem....as if you were to tell them to another person. • Remember an algorithm is a sequence of step by step instructions for performing some tasks CS161 Topic #2

9. For Example...solve a problem • Convert inches to millimeters • First understand the problem • where do the inches come from (the user) • what is the math needed for the conversion • mm = 25.4 times inches • how do we want to display the results • 2in convert to 50.8mm CS161 Topic #2

10. Convert inches to millimeters • Next, write the algorithm • Step 1: Welcome the user • tell them what to expect • tell them the purpose of the program CS161 Topic #2

11. Convert inches to millimeters • Step 2: • Get the number of inches from the user • display a prompt asking the user to enter • read in the number of inches • display what was read (echo) • ask the user if this is really correct (confirm) • if not, repeat this step until the user is satisfied CS161 Topic #2

12. Convert inches to millimeters • Continuing with Steps 3 and 4: • Convert the number of inches to mm • mm = 25.4 times inches • Display the results • Provide a sign-off message CS161 Topic #2

13. Convert inches to millimeters • The next step is to turn this into a C++ program! • All programs have the following “form” #include <iostream> using namespace std; //header comments... int main() { //program body goes here... return 0; } CS161 Topic #2

14. Convert inches to millimeters #include <iostream> using namespace std; // *********************************** // Karla S. Fant // CS161 Programming Assignment #0 // Purpose of this program is to convert // inches entered in by the user into // millimeters and display the results // ********************************** int main() { CS161 Topic #2

15. (Different Kind of Comment...) #include <iostream> using namespace std; /* *********************************** Karla S. Fant CS161 Programming Assignment #0 Purpose of this program is to convert inches entered in by the user into millimeters and display the results ********************************* */ int main() { CS161 Topic #2

16. Convert inches to millimeters //Define variables float inches; //to save # inches float mm; //to save the result //Step #1, welcome the user cout <<“Welcome! We will be converting” <<“ inches to mm today” <<endl; CS161 Topic #2

17. (A different way to do this...) //Define variables float inches, //to save # inches mm; //to save the result //Step #1, welcome the user cout <<“Welcome! We will be converting”; cout <<“ inches to mm today” <<endl; (NOTE: endl is end followed by a letter l) CS161 Topic #2

18. Convert inches to millimeters //Step #2, Get the input (prompt, read) cout <<“Please enter the number of inches” <<“ that you wish to convert: “; cin >> inches; //read the # inches //echo what was entered cout <<“You entered: “ <<inches <<“in” <<endl; CS161 Topic #2

19. Convert inches to millimeters //Step #3 Convert inches to millimeters mm = 25.4 * inches; //Step #4 Display the results cout <<inches <<“in converts to “ <<mm <<“mm” <<endl; //Step #5 Sign off message cout <<“Thank you for using CONVERT” <<endl; return 0; } CS161 Topic #2

20. CS161 Introduction to Computer Science ASSIGNMENTS!!! CS161 Topic #2

21. Programming Assignment #1 • First, get an ODIN account • Next, learn how to login • Try sending email! • Learn how to exit the ODIN menu and enter the UNIX shell • Meet with TA’s to get a hand’s on tutorial. Their office hours are posted on the web site: www.cs.pdx.edu/~karlaf CS161 Topic #2

22. Programming Assignment #1 • Put the #include <iostream> in column #1 • endl is “e n d” followed by lower case L • spaces inside double quotes ARE important CS161 Topic #2

23. Steps to Enter a Program • Login to ODIN • Exit the Menu • Now you are at the UNIX prompt • It is time to enter your program! vi prog1.cpp <enter> • Now it is time to start inserting our program. To do so, type i, for insert: CS161 Topic #2

24. Steps to Enter a Program • Now start typing your program. Line by line. When done hit the escape key. • If the program is perfect, it is time to write it to the file. Type :w <enter> • To quit the editor, type :q <enter> CS161 Topic #2

25. Steps to Enter a Program • We are now back to the UNIX prompt. To compile the program we type the following. g++ prog1.cpp <enter> • At this point, there will either be error messages displayed (with line numbers), or not (if it is correct!). CS161 Topic #2

26. Steps to Enter a Program • To fix a program, we must edit it. Type: vi prog1.cpp <enter> • Now, if you want to go to the line where the error occurred, type the line number followed by the enter key. For example, to go to line number 10 type: 10 <enter> CS161 Topic #2

27. Steps to Enter a Program • To add something at the end (like a semicolon), type a for append: • Now you are in append mode. You can type what you want. When you are done typing hit the escape key • When you are done, type the following to write the changes back to the file and quit the editor :wq! <enter> CS161 Topic #2

28. Steps to Enter a Program • Other things to type while in the editor: • h goes left • k goes up • j goes down • l goes right • x delete the character you are at • dd delete the line that you are at CS161 Topic #2

29. Steps to Enter a Program • Again, we are at the unix prompt. To compile your program type: g++ prog1.cpp <enter> • If it compiles without any errors, it is time to run the program to see it actually work! Type ./a.out <enter> CS161 Topic #2

30. CS161 Introduction to Computer Science Are you Ready? CS161 Topic #2