cs201 introduction to computing @ sabancı university 1 announcements l midterm dates ä first...

CS201 Introduction to Computing @ Sabancı University 1

Announcements Midterm Dates

First Midterm Exam: November 7, 2015, Saturday, 14:00 – 16:00 Second Midterm Exam: December 5, 2015, Saturday, 10:00 – 12:00

Extra lecture on Wednesday between 17:40 – 19:30 in FASS G062. Same lecture will be repeated on the same day 19:40 – 21:30 in FASS

G062. Office Hours have started, schedule is at the TA web site, which is

reachable from course web site. Anyone who have not formally registered to the course until the end of

add drop should see me during the break. Email list is active

[email protected] Service provided by SUCourse; Your sabanciuniv accounts are

registered We’ve already sent some emails to this list. Did you get them? We will make announcements to the list and sometimes to

SUCourse. Check your emails and SUCourse regularly Please do not subscribe this list address to some other lists


Announcements Our development environment is MS Visual Studio/C++ 2012 under MS

Windows. Any Windows is OK but for Visual Studio you have to use 2012. Older or

newer versions may create consistency problems with our grading system. Other C++ compilers and development environments also have the same

potential for inconsistency.• Thus your homework that works in your compiler may not work in ours. • If you have to use another development environment for some reason, you have

to make sure that it also works under Windows and MS Visual Studio 2012 before submission. This is your responsibility.

The "robot" application that we will see next week (and also HW3 and HW5 will be about it) designed only for MS Windows and Visual Studio; you will not be able to use it in another platform.

Any Mac users encountered problem during installation? Windows 8 is no longer available at university's Software server?

• Due to licence restrictions You can get Windows from Microsoft Dreamspark service

• To do so first you have write IT to get an account and then wait for Microsoft for activation. This process may take a couple of days. Details are here http://mysu.sabanciuniv.edu/it/tr/microsoft-software/dreamspark


Announcements First homework is due on October 7, Wednesday, 17:00

Submit to SUCourse Strictly follow the submission guideline provided in the homework

specification Write comments in your program (this will affect your grade) Use meaningful identifier names and have a proper indentation (these

will also affect your grade) New (Second) homework will be assigned this week Stopping at the end of the program execution

If you run under the debugger (Ctrl+F5), you will automatically get this prompt at the end of the execution and the program waits there:• Press any key to continue . . .

However, if you run with F5 only, you will NOT get this prompt and the console screen (the black screen) disappears after the execution. This is not a problem of your code.

You can add the following at the end of your code (before return 0;) to get the same effect:cin.ignore();cin.get();


Announcements A general question about the first homework

What if the total number of points cannot be reached with integer number of wins and draws?• E.g. if total points is 18, one win is 5 and one draw is 2 points. Max.

number of wins is 3 , but the remaining 3 points cannot be obtained with integer number of draws.

• In the homework specification we explicitly stated that such cases will not happen. Thus you can assume that there always be integer solutions in the test cases.

Another issue about the first homework There must be four inputs only

• First one is the name of the team• Second one is the amount of points given to a win• Third one is the amount of points given to a draw• Fourth one is the total points to be collected

You have to preserve this order No other inputs are allowed. Otherwise, our system cannot process

your homework


Chapter 2 – Continued / Functions Main function A program is a collection of functions and classes

main and other programmer defined functions• only main is executed automatically when the program starts• other functions must be called to be executed

Programmer-defined functions piece of code to do a specific job must be declared before using (this is named as calling a function)

return-type function-name (parameters){ local variables

statements}

to execute a function just write its name (and arguments for parameters)• When a function is called, execution order temporarily jumps to function• after the function ends, execution order goes back to the caller

For the time being• return type is void – that means returns nothing• no parameters (we will see parametric functions today)


Functions – A simple example

Without function#include <iostream>using namespace std;

//traditional first program

int main(){

cout << "Hello world" << endl;return 0;

}

#include <iostream>using namespace std;

//traditional first program

void Hello(){

cout << "Hello world" << endl;

}

int main(){

Hello();return 0;

}

With function

Output is the same in both case

Hello world


Why Functions?

Divide and Conquer technique divide your problem into small ones write one function for each combine them in the main program

Provides modularity when you need to replace a piece of code, you just

change a function you may not need to change the main program

Reuse the same code piece several times avoid repeating the same code


With no Functions#include <iostream>using namespace std;int main(){ cout << " |||||||||||||||| " << endl; cout << " | | " << endl; cout << " | o o | " << endl; cout << " _| |_ " << endl; cout << "|_ _|" << endl; cout << " | |______| | " << endl; cout << " | | " << endl; return 0;} Prints head, but not so modular

changing the head style requires an update in main. Is this bad? • in this “small” example, need for modularity may not be clear, but

in long programs you will need it. Several heads (like a totem)?

you have to duplicate the same code


With FunctionsSee parts.cpp for the entire program

#include <iostream>using namespace std;// functions appear here

int main(){

Hair(); Sides();Eyes(); Ears(); Smile();Sides();return 0;

} Although more complicated, what are advantages of this main over one in

which several output statements appear in main? modularity

• changing the head style = changing function(s)• what about eyeglasses? mustache? (let’s do one)

Code re-use (i.e. NOT duplicating the code unnecessarily)• multiple heads (totem poles)? (let’s do one)


Functions with Parameters Functions are useful, parameterized functions might be more useful

You may need to pass data into a function when you call it Consider a generic function to calculate the area of any circle and

display it how will the function know the radius? solution: parameters

• function is defined without knowing the value of the radius

• value of radius is passed to the function when it is called parameters are defined similar to variables

type name

Example:

double radius You may have several

parameters separated by comma

return-type func-name (type param1, type param2,…){ local variables statements}


Area calculation using parameterized function

#include <iostream>using namespace std;// area calculation program that employs functions

void calculate_area (float radius){

float area;

area = 3.14*radius*radius;cout << "The area of a circle with radius " << radius << " is " << area << endl;

}

int main(){

float r;r = 3;calculate_area(r);calculate_area(2.5);calculate_area(r/2);

return 0;}





float area;


}

int main(){


return 0;}

radius is 3

The area of a circle with radius 3 is 28.26

Output Screen





float area;


}

int main(){


return 0;}

radius is 2.5


Output Screen

The area of a circle with radius 2.5 is 19.625





float area;


}

int main(){


return 0;}

radius is 1.5


Output Screen




Functions with Parameters (continued) Parameters and Arguments

parameter is the generic name used in function • radius in the calculate_area function

argument is the value passed to function while it is called• 2.5• r (actually current value of r is passed)• r/2 (actually current value of r/2 is passed)

Parameter list provides type and name of the parameters Argument type must match parameter type

Functions may have multiple parameters corresponding arguments are separated by commas

• in the same order of parameter list• be careful about the type matching

we will see examples later on Functions may call other functions (have seen in the totem

example and will see in the next example)


Functions with Parameters (continued) Parameters versus Local Variables

Parameters and defined and used locally, but their initial value comes from the caller function via arguments

Local variables are defined and used in the function locally• But the initial value does not come from the caller function

While designing your functions, think carefully about local variables and parameters If you need to pass the initial value from the caller function,

then it should be a parameter. If you won’t pass the initial value, then it should be a local

variable. Example: in calculate_area function

• area is a local variable since we do not pass its initial value from main• radius is a parameter since we need to pass its initial value from main

Unnecessary parameters may cause problems and grade reduction (for homework)


Old McDonald’s Farm Aim is to have a modular program (with functions) to display the song

each verse repeats using a different animal refrain parts repeat within verses A partial output (with two animals only) below

Old MacDonald had a farm, Ee-igh, Ee-igh, oh!And on his farm he had a cow, Ee-igh, Ee-igh, oh!With a moo moo hereAnd a moo moo thereHere a moo, there a moo, everywhere a moo mooOld MacDonald had a farm, Ee-igh, Ee-igh, oh!

Old MacDonald had a farm, Ee-igh, Ee-igh, oh!And on his farm he had a cat, Ee-igh, Ee-igh, oh!With a meow meow hereAnd a meow meow thereHere a meow, there a meow, everywhere a meow meow Old MacDonald had a farm, Ee-igh, Ee-igh, oh!


Old McDonald’s Farm (Design of Functions)

Which functions do we need? a function for only “Ee-igh, Ee-igh, oh!” a function for the refrain (nakarat) a function for “And on his farm ...” line

• animal is parameter a function for “With a ...”, “And a ...”, “Here a ...” lines

• noise of the animal is a parameter a function for the whole verse

in the main program call the verse function with several animal and noise arguments


Old McDonald’s Farm (Program) See oldmac2.cpp Remarks

functions call functions• Refrain calls EiEio• Verse calls Refrain

Verse has two parameters• therefore it is called using two arguments –first one is for

animal, second is for noise• order of arguments is important

animal is used as parameter in two functions.• Should we need to use the same parameter name in both

cases? Or can we use different names in two different functions?

• Same questions are valid for noise as well.• Answer is “Yes we can use different names”. Let’s do and see.

Can we input animal and noise? of course yes (will do next)


Programs that Respond to Input Programs without input always give the same results

values are hardcoded For new values

change the program, compile and run again• not a good programming practice

Allow the user to input values that generate output• from keyboard, using cin • we did this in the first circle area calculation program

Sequential model of programming: input, process, output Input: information provided from the user (outside

world) Process: Information is processed Output: display the result


Mac Donald’s farm with user input We want the user to enter/input values for animal and noise

Enter the name of an animal: sheepEnter noise that a sheep makes: baahOld MacDonald had a farm, Ee-igh, Ee-igh, oh!And on his farm he had a sheep, Ee-igh, ee-igh, oh!With a baah baah hereAnd a baah baah thereHere a baah, there a baah, everywhere a baah baahOld MacDonald had a farm, Ee-igh, Ee-igh, oh!

We’ll pass the user-entered values to the Verse function The input stream cin takes input from the keyboard using

operator >> Values that are input are stored in variables and then

passed to function verse as arguments see macinput2.cpp


Mac Donald’s farm revisited

// other functions goes here (see macinput2.cpp)void Verse(string animal, string noise){ // this function doesn’t change// see the source code for the function code}

int main(){ string animal; // variable for name of animal string noise; // variable for noise it makes cout << "Enter the name of an animal: "; cin >> animal; cout << "Enter noise that a " << animal << " makes: "; cin >> noise; Verse(animal,noise); return 0;}


Analysis of the Run1. input value “sheep” is stored in variable animal

2. input value “baah” is stored in variable noise

3. “sheep” and “baah” values are passed to function Verse as arguments as well as used in cout in main


Variables (review from previous lectures) Variables are used to store values in memory

memory locations that are accessed using a name in the program

Each variable has a type, a name (identifier), and a value

Methods to give values to variables Assignment, using = Input, using cin

Definition: type variable_names_separated_by_comma;


Where to define variables You can define variables anywhere within a function

provided that it is defined before the first use Two common conventions for the place of variable definition

At the beginning of the function in which they’re used: { string animal,noise; cout << "enter animal "; cin >> animal; cout << "enter noise a " << animal << " makes "; cin >> noise; } Just before the first place that they’re used: { cout << "enter animal "; string animal; cin >> animal; cout << "enter noise a " << animal << " makes "; string noise; cin >> noise; }


Where to define variables NO GLOBAL VARIABLES A global variable is a variable defined outside the

function bodies They can be used in all functions without definition

That is why it is the #1 enemy of parameters If you use global variables, you violate the

independence property of functions and may lose your control in big programs

Thus, IT IS FORBIDDEN TO USE GLOBAL VARIABLES If you use a global variable in homework and exams,

your grade will be reduced! At the end of the course, I will formally teach global

variable concept. After that, you will need to know what global variable is and apply them

whenever you are asked for, but not without permission!


Variable Initialization Variables have garbage (junk values) until

they are assigned a value using assignment operatormyint = 5;

or an input is stored into them (using cin statement)cin >> myint;

Variables must be given a value before you refer to its value for the first time in an expression or an output statement or as an argument to a function idea behind this rule: you can never know what is inside of an

uninitialized variable! not a syntax error, compiler may or may not warn you!

You may initialize variables at the declarationint myint = 5;

After initialization, you may change the value stored in a variable several times that is why they are named as “variable”


Scope of a Variable and Parameter

Not explained in the book in this way Complex rules. Now I give a simple version! RULE 1: A variable or parameter can be referred only within

the function in which it is declared e.g. you cannot refer the variable animal in function eieio

RULE 2: A specific identifier can be used several times in different functions as variable or parameter names. Those are actually different variables/parameters. e.g. animal and noise are used both in main (as variable)

and Verse (as parameter) RULE 3: A specific identifier must be unique within a function Detailed scope rules will be given later in this course


Reading Assignment

Section 3.3 Case Study: Pizza Slices Similar to circle area calculation program Run the program pizza.cpp

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