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”);

}

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 write to end create new

fclose(file pointer)

Pretty basic.

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%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 ); }

}

QuizKelly 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”, 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”, 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(“Enter data separated by spaces:”);

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

}

Quiz

Can you write a program that asks the user for their Name Phone Number Bank account balanceAnd then prints this information to a data file called accounts.dat ?

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.c_str();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.c_str();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 TypesTYPE 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 onint 4 bytes -2,147,483,648 to 2,147,483,647short 2 bytes -32,768 to 32,767long 4 bytes -2,147,483,648 to 2,147,483,647float 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

If statements

if(condition)statement;else if (condition)statement;

condition ? expr1 : expr2 ex. z = ( x > y ) ? y : x ; cannot do

(x>y) ? count << “x is greater than y.” : cout << “x isn’t greater than y.”

Switch-case statements

switch(expression){case expr1:

statement;break;

case expr2:statement;break;

case expr3:statement;break;

default:statementsbreak;

}

Loops

while (condition){

statements;}

do{

statements;}while(condition);

Loops

for (initialization; condition; expression)

{statements;

} Incrementing: Prefix and Postfixint x = 5;int y = 6;int z = y++ //z=6, y=7 postfix

operator int z = ++x //z=6, x=6 prefix

operator

Branching statementsKeyword Purposebreak Exits the nearest enclosing

“switch” statement or iteration statement

continue Starts the next loop of the nearest enclosing iteration statement

goto Jumps to a particular place in your code

return Ends a function and returns a value

FOR LOOP TEST

Can you write a program that prints out the following?

0 1 2 3 4 5 6 7 8 9

Answer

for ( int count = 0; count < 10; count ++)

{cout <<count<<“”;

}

Other Challenge questions for Loops1. Write a conditional statement that will assign

x/y to x if y doesn’t equal 0.

2. Write a while loop that calculates the summative of positive integers from 1 to some number n.

3. Write a conditional statement that assigns x*y if x is even; otherwise , if x is odd and y doesn’t equal 0, assign x to x/y; if neither of the preceding cases is true, output to the screen that y is equal to 0.

How to declare and implement functions Function declaration Function definition Function call

#include <iostream>using namespace std;

int add(int a, int b);

int main(void){

int number1, number2;cout << “Enter the first value to be summed:”’

cin >> number1;cout << “\nEnter the second:”;

cin >> number2;cout << “\n The sum is: “ << add (number1, number2) <<endl;

}

int add(int a, int b){

return a+b;}

Functions Challenge

Write a function, called multiply that multiplies two numbers and returns the result

OOP Declare classes Create objects

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

implementation of a class behind an interface so that the user of the class corrupt that data

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;

}

Advanced Data Types

Arrays Pointers

How to create arrays

data_type array_name [number-of-elements];

Two Dimensional Arrayarray_type array_name [number_ofelements1]

[number_of_elements2];

How to create pointers

type* pointer_name;

ex. int my_int;int* my_int_pointer =

&my_int;

Assigns the address of my_int to the pointer

Useful string functions

Copying strings from one to another char* strcpy(char* p, const char* q); char s[6];

strcpy(s, “Hello”);

To combine strings char* strcat(char* p, const char* q); char s[12] = “Hello”

strcat(s, “World”);

Useful string functions

To copy n characters from q to the of p.

char* strncpy(char* p, const char* q, int n); char s [7] = “Say “;

char t[] = “Hi”;strncpy (s, t, 2)

Challenge question

Can you write a program using C++ that uses a FOR loop to initialize a 2D array that looks like the following {0,5,10,15}{0,2,4,6}

Answer

#include<iostream>using namespace std;int main(void){int array[4][4];

for( int i = 0; i< 5; i++){

Basics of C++

Basic framework for a program How to Comment How to Print How to store variables How to Print stored variables How to find the size of a variable How to convert from one data type

to another How to Declare Constants

Basics of C++

If statements Conventional Using conditional operator

Switch-case statements Loops

While Do-While For

Branching statements

Basics of C++

How to declare and implement functions

How to create arrays How to create pointers Useful string functions Classes

How to Comment

//this is how you comment /*this is how

you comment */ Use for Multiple lines

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{

public:int anInt;

}

class aDerivedClass : public aClass{

protected:float aFloat;

};

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)