cs161 topic #21 cs161 introduction to computer science topic #2

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CS161 CS161

Introduction to Introduction to Computer ScienceComputer Science

Topic #2

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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

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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

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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

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• 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

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• 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

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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!

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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

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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

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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

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• 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

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• 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

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• 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;

}

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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() {

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(Different Kind of Comment...)

#include <iostream>using namespace std;/* ***********************************

Karla S. FantCS161 Programming Assignment #0Purpose of this program is to convertinches entered in by the user intomillimeters and display the results********************************* */

int main() {

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//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;

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(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)

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//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;

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Convert inches to millimeters//Step #3 Convert inches to millimetersmm = 25.4 * inches;

//Step #4 Display the resultscout <<inches <<“in converts to “ <<mm <<“mm” <<endl;

//Step #5 Sign off messagecout <<“Thank you for using CONVERT” <<endl;return 0;}

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ASSIGNMENTS!!!

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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

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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

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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:

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• 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>

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• 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!).

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• 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>

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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>

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• 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

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• 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>

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Are you Ready?

cs161 topic #21 cs161 introduction to computer science topic #2

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