REACH CECS 130 Exam 2 Test Review

C - Files

Do you know the syntax for each of these, used to read and write to data files?

Pointers: think of it as the memory address of the file

fopen()

fclose()

fscanf()

fprintf()

fopen(“file name”, “Mode”) fopen() returns a FILE pointer back to the pRead

variable

#include <cstdio>

Main(){

FILE *pRead;pRead = fopen(“file1.dat”, “r”);

if(pRead == NULL) printf(“\nFile cannot be opened\n”);else printf(“\nFile opened for reading\n”);

}

What does this code do?

int main (){ FILE * pFile; char c; pFile=fopen("alphabet.txt","w");//Open with write access for (c = 'A' ; c <= 'Z' ; c++) { putc (c , pFile);//works like fprintf } fclose (pFile); return 0;}

Common Text File Modes

Mode Meaning Already Exists Does Not Exist

“r” Open a file for reading read from start error

“w” Create a file for writing destroy contents create new

“a” Append to a file write to end create new

“r+“ Open a file for read/write read from start error

“w+“ Create a file for read/write destroy contents create new

“a+“ Open a file for read/write appending

write to end create new

“b” Combined with any mode enables user to work with binary files.(rb, wb, r+b, etc.)

fclose(file pointer)

Pretty basic. Always close files when you use fopen.

fscanf(FILE pointer, “data type”, variable in which to store the value)

Reads a single field from a data file

“%s” will read a series of characters until a white space is

found

can do fscanf(pRead, “%s\t%s”, name, hobby);

#include <stdio.h>

Main(){ FILE *pRead;

char name[10]; pRead = fopen(“names.dat”, “r”);

if( pRead == NULL ) printf( “\nFile cannot be opened\n”); else printf(“\nContents of names.dat\n”); fscanf( pRead, “%s”, name );

while( !feof(pRead) ) { printf( “%s\n”, name ); fscanf( pRead, “%s”, name ); }

}

Quiz

Kelly 11/12/86 6 LouisvilleAllen 04/05/77 49 AtlantaChelsea 03/30/90 12Charleston

Can you write a program that prints out the contents of this information.dat file?

#include <stdio.h>

Main(){ FILE *pRead;

char name[10]; char birthdate[9]; float number; char hometown[20];

pRead = fopen(“information.dat”, “r”);

if( pRead == NULL ) printf( “\nFile cannot be opened\n”); else fscanf( pRead, “%s%s%f%s”, name, birthdate, &number, hometown );

while( !feof(pRead) ) { printf( “%s \t %s \t %f \t %s\n”, name, birthdate, number, hometown ); fscanf( pRead, “%s%s%f%s”, name, birthdate, &number, hometown ); }

}

fprintf(FILE pointer, “list of data types”,list of values or variables)

The fprintf() function sends information (the arguments) according to the specified format to the file indicated by stream. fprintf() works just like printf() as far as the format goes.

#include <stdio.h>

Main(){

FILE *pWrite;

char fName[20];char lName [20];float gpa;

pWrite = fopen(“students.dat”,”w”);

if( pWrite == NULL )printf(“\nFile not opened\n”);

elseprintf(“\nEnter first name, last name, and GPA

separated”);printf(“\nEnter data separated by spaces:”);

scanf(“%s%s%f”, fName, lName, &gpa);fprintf(pWrite, “%s \t %s \t % .2f \n”, fName, lName, gpa);fclose(pWrite);

}

C++ Input/Output

Summary Include #include <iostream> directive

at beginning of program Use cin to take data from user Use cout to display data on screen▪ Display multiple strings and integers in the

same cout statement by separating items with <<

C++ Input/Output Example#include <iostream>#include<string>using namespace std;

string name = “”;

int main(void){

cout<<“What is your name?”;cin>>name;cout<<endl<<“Hello ”<<name;return 0;

}

Can you predict the printout?

#include <iostream>using namespace std;int x = 25;string str2 = “This is a test”;

int main( void ){

cout<<“Test”<<1<<2<<“3”;cout<<25 %7<<endl<<str2;return 0;

}

Answer

Test 1234This is a test

Data

How a computer stores data in its internal memory RAM (Random-Access Memory) - temporary ROM (Read-Only Memory) – non volatile Store data in bytes

How you store data temporarily Create variables based on fundamental

types (bool, char, int, float) constants: #define CONSTNAME value sizeof()

Variable Types

TYPE SIZE VALUES

bool 1 byte true (1) or false (0)

char 1 byte ‘a’ to‘z’ , ‘A’ to ‘Z’, ‘0’ to ‘9’, space, tab, and so on

int 4 bytes -2,147,483,648 to 2,147,483,647

short 2 bytes -32,768 to 32,767

long 4 bytes -2,147,483,648 to 2,147,483,647

float 4 bytes + - (1.2 x 10^-38 to 3.4 x 10^38)

double 8 bytes +- (2.3 x 10^-308 to -1.7 x 10^308)

Control Statements – Boolean Operators

What do each of the following evaluate to?1. long elves = 8;

int dwarves = 8;if(elves==dwarves) //true or false?if(elves!=0) //true or false?

2. int elves = 4;int dwarves = 5;if(dwarves > (2/3)) //true or false?

3. if(0 < x < 99) //true or false?4. if(0<= (0<1))//true or false?

Control Statements – Boolean Operators -Answers

What do each of the following evaluate to?1. long elves = 8;

int dwarves = 8;if(elves==dwarves) //trueif(elves!=0) //true

2. int elves = 4;int dwarves = 5;if(dwarves > (2/3)) //true

3. if(0 < x < 99) //true …TRUE (1) and FALSE (0) < 994. if(0<= (0<1))//true

OOP

Declare classes Create objects

3 MAIN PRINCIPLES OF OOP Data abstraction – hiding data members and

implementation of a class behind an interface . Encapsulation – each class represents a

specific thing or concept. Multiple classes combine to produce the whole

Polymorphism-objects can be used in more than one program

Classes

Classes are general models from which you can create objects

Classes have data members either data types or methods

Classes should contain a constructor method and a destructor method

See handout for example of a program that utilizes a class

Declaring Classes

class ClassName{

memberList};

memberList can be either data member declarations or method declarations

Class Declaration ExampleClass Bow{

//data member declarationsstring color;bool drawn;int numOfArrows;

Bow(string aColor); //constructor~Bow(); //destructor

//methodsvoid draw();int fire();

};

Creating Methods

Return_type ClassName::methodName(argumentList)

{methodImplementation

}

Methods Creation Example//draws the bowVoid Bow::draw(){

drawn = true;cout<< “The “<<color<<“bow has been drawn.”<<endl;

}

Namespaces

Used to create functions, classes, and variables of the same name

Ex.

Namespace combat{

void fire()}Namespace exploration{

void fire()}

Namespaces

To call a namespace combat::fire()

Say (to avoid having to put combat:: every time

using namespace combat;

fire()

Inheritance

class aClass// Base class{

public:int anInt;

}

class aDerivedClass : public aClass//Derived class

{protected:

float aFloat;};

Inheritance for Mammals Kingdome

#include <iostream.h>enum BREED { YORKIE, CAIRN, DANDIE, SHETLAND, DOBERMAN, LAB };class Mammal{public: Mammal(); // constructors ~Mammal();//destructor //accessorsint GetAge()const;void SetAge(int);int GetWeight() const;void SetWeight();//Other methodsvoid Speak();void Sleep();protected:int itsAge;int itsWeight;};class Dog : public Mammal {public: Dog(); // Constructors~Dog(); // AccessorsBREED GetBreed() const; void SetBreed(BREED); // Other methods // WagTail(); // BegForFood(); protected: BREED itsBreed;};

Animals

Mammals

Reptiles

Horse Dog

Hound Terrier

Yorkie Cairn

Private vs. Protected

Private members are not available to derived classes. You could make itsAge and itsWeight public, but that is not desirable. You don't want other classes accessing these data members directly.

What you want is a designation that says, "Make these visible to this class and to classes that derive from this class." That designation is protected. Protected data members and functions are fully visible to derived classes, but are otherwise private.

Overriding Functions

When do we need to override functions? If you are a programmer example. If we consider “Woof” of the dog as

speak. When a derived class creates a

function with the same return type and signature as a member function in the base class, but with a new implementation, it is said to be overriding that method.

Overriding example #include <iostream.h> enum BREED { YORKIE, CAIRN, DANDIE, SHETLAND, DOBERMAN, LAB }; class Mammal { public: // constructors Mammal() { cout << "Mammal constructor...\n"; } ~Mammal() { cout << "Mammal destructor...\n"; } //Other methods void Speak()const { cout << "Mammal sound!\n"; } void Sleep()const { cout << "shhh. I'm sleeping.\n"; } protected: int itsAge; int itsWeight; };

class Dog : public Mammal { public: // Constructors Dog(){ cout << "Dog constructor...\n"; } ~Dog(){ cout << "Dog destructor...\n"; } // Other methods void WagTail() { cout << "Tail wagging...\n"; } void BegForFood() { cout << "Begging for food...\n"; } void Speak()const { cout << "Woof!\n"; } private: BREED itsBreed; }; int main() { Mammal bigAnimal; Dog fido; bigAnimal.Speak(); fido.Speak(); getchar(); return 0; }

Overloading Functions

When you overload a method, you create more than one method with the same name, but with a different signature. When you override a method, you create a method in a derived class with the same name as a method in the base class and the same signature.

Overloading example

#include<iostream.h>

int area(int x); // square areaint area(int x,int y); //triangle areafloat area(int x,int y, int radius); //circle area

int main(){ int x=4, y=5, rad=3; cout<<"The Square area is :"<<area(x); cout<<"\nThe Triangle area is :"<<area(x,y); cout<<"\nThe Circle area is :"<<area(x,y,rad); getchar(); return 0;}

int area(int x) // square area{ return x*x; }

int area(int x,int y ) //triangle area{ return x*y; }float area(int x,int y, int radius) //circle area{ return radius*radius*3.14; }

Output:The Square area is: 16The Triangle area is :20The Circle area is: 28.26

Another overloading example

#include <iostream.h>class Mammal {public:void Move() const { cout << "Mammal move one step\n"; }void Move(int distance) const { cout << "Mammal move ";cout << distance <<" _steps.\n"; }protected:int itsAge;int itsWeight;};class Dog : public Mammal {public:// You may receive a warning that you are hiding a function!void Move() const { cout << "Dog move 5 steps.\n"; }}; int main() {Mammal bigAnimal;Dog fido;bigAnimal.Move();bigAnimal.Move(2);fido.Move(8);fido.Move();return 0;} // Can you spot any problem/s in the last 4 lines ?

Output:Mammal move one stepMammal move 2 steps.Dog move 5 steps

Virtual Functions To call a function you’ve overridden in a derived class you need to

use virtual functions. Example:struct Base { virtual void do_something() = 0; }; struct Derived1 : public Base { void do_something() { cout << "I'm doing something"; } }; struct Derived2 : public Base { void do_something() { cout << "I'm doing something else"; } }; int main() { Base *pBase = new Derived1; pBase->do_something();//does something delete pBase; pBase = new Derived2; pBase->do_something();//does something else delete pBase; return 0; }

Another Example

Output: (1)dog (2)cat (3)horse (4)pig: 1(1)dog (2)cat (3)horse (4)pig: 2(1)dog (2)cat (3)horse (4)pig: 3(1)dog (2)cat (3)horse (4)pig: 4(1)dog (2)cat (3)horse (4)pig: 5Woof!Meow!Winnie!Oink!Mammal speak!

#include<stdlib.h>#include <iostream.h> class Mammal { public: Mammal():itsAge(1) { } ~Mammal() { } virtual void Speak() const { cout << "Mammal speak!\n"; } protected: int itsAge; };

class Dog : public Mammal { public: void Speak()const { cout << "Woof!\n"; } };

class Cat : public Mammal { public: void Speak()const { cout << "Meow!\n"; } };

class Horse : public Mammal { public: void Speak()const { cout << "Winnie!\n"; } };

class Pig : public Mammal { public: void Speak()const { cout << "Oink!\n"; } };

int main() { Mammal* theArray[5]; Mammal* ptr; int choice, i; for ( i = 0; i<5; i++) { cout << "(1)dog (2)cat (3)horse (4)pig: "; cin >> choice; switch (choice) { case 1: ptr = new Dog; break; case 2: ptr = new Cat; break; case 3: ptr = new Horse; break; case 4: ptr = new Pig; break; default: ptr = new Mammal; break; } theArray[i] = ptr; } for (i=0;i<5;i++) theArray[i]->Speak(); system("pause");return 0; }

Virtual functions, When to use them?

Only if you have to redefine a function in a Derived class that is already defined in Base Class, otherwise, it’s just extra resources when executed.

Pointers of type base class

#include <iostream>using namespace std;

class CPolygon { protected: int width, height; public: void set_values (int a, int b) { width=a; height=b; } };

class CRectangle: public CPolygon { public: int area () { return (width * height); } };

class CTriangle: public CPolygon { public: int area () { return (width * height / 2); } };

int main () { CRectangle rect; CTriangle trgl; CPolygon * ppoly1 = &rect; CPolygon * ppoly2 = &trgl; ppoly1->set_values (4,5); ppoly2->set_values (4,5); cout << rect.area() << endl; cout << trgl.area() << endl; getchar(); return 0;}

Templates

Used in place of a specific data type. For example, use a template to add data types together, whichever data type the user wishes (i.e. integers, floats)

Function Template

#include <iostream>using namespace std;

template <class T>T GetMax (T a, T b) { T result; result = (a>b)? a : b; return (result);}

int main () { int i=5, j=6, k; float l=10.5, m=5.6, n; k=GetMax<int>(i,j); n=GetMax<float>(l,m); cout << k << endl; cout << n << endl; getchar(); return 0;}

Output:610.5

Other Template cases

int i;long l;k = GetMax (i,l); This would not be correct, since our GetMax function template expects two arguments of the same type.But if we did the following:template <class T, class U> T GetMin (T a, U b) { return (a<b?a:b); }Then we could call the function like this:int i,j;long l;i = GetMin<int,long> (j,l); Or simply:i = GetMin (j,l);

Class Template

#include <iostream> using namespace std; template <class T> class mypair { T a, b; public: mypair (T first, T second) {a=first; b=second;} T getmax (); }; template <class T> T mypair<T>::getmax () { T retval; retval = a>b? a : b; return retval; } int main () { mypair <int> myobject (100, 75); cout << myobject.getmax(); return 0; }

Output:100

Templates cntd.

mypair<int> myobject (115, 36); This same class would also be used to create an object to store any other type:mypair<double> myfloats (3.0, 2.18);

More on Templates

#include <iostream>using namespace std;

// class template:template <class T>class mycontainer { T element; public: mycontainer (T arg) {element=arg;} T increase () {return ++element;}};

// class template specialization:template <>class mycontainer <char> { char element; public: mycontainer (char arg) {element=arg;} char uppercase () { if ((element>='a')&&(element<='z')) element+='A'-'a'; return element; }};

int main () { mycontainer<int> myint (7); mycontainer<char> mychar ('j'); cout << myint.increase() << endl; cout << mychar.uppercase() << endl; return 0;}

Output:8J

Questions??Good Luck on your Test