C/C++ Programming on Hobbes(Unix) Omar Haque Csci 169 Spring 2003.

C/C++ Programming on Hobbes(Unix)

Omar Haque

Csci 169

Spring 2003

Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

TA Information

• Name: Omar Haque

• Email: [email protected]

• Office Phone: not ready

• Office Room: not ready

• Office Hours: Tuesday 1pm –3pm

mailto:[email protected]


Open Lab

• Tuesday – Han Young will run the lab– I will be there to help out

• Friday– Semi lecture in lab– Help on class wide problems


ANSI

• American National Standards Institute

• 1990 approved standard for C

• 1997 approved standard for C++


First C Program

/*Comment*/

#include <stdio.h> /*standard input/output header file*/

main()

{

/*declarations*/

int number1, number2;

number2 = 5;

printf("Enter a number\n");

scanf("%d", &number1);

printf("Number 1 is %d\n", number1);

printf("Number 2 is %d\n", number2);

return 0;

}


Compiling and Execute C Program

• % gcc filename.c –o outputfile– GNU C compiler– Preprocess, compile, link

• % ./outputfile


First C++ Program

//comment

#include <iostream.h>

int main ()

{

//declarations

int number1, number2;

number2 = 5;

cout <<"Enter Number 1 ";

cin >> number1;

cout << "Number 1 is "<< number1 << endl;

cout << "Number 2 is "<< number2 << endl;

return 0;

}


Compile and Execute C++

• % CC hello.cpp –o outputfile– Sun C++ compiler

• % g++ hello.cpp –o outputfile– GNU C++ compiler

• % ./outputfile


Comments

• C requires comments to be delimited by /* and */

• C++ allows // for one line comments

• C++ also allows /* */


Variables, Identifiers

• Variable – piece of memory that is used to hold a value

• Identifiers:– Combination of letters, digits, and underscores– Variable names should start with letter or digit

• C and C++ are case sensitive


Data Types

• char - 1 byte = 8bits

• int – (system dependent)– short 2 byte– long 4 byte

• float – 4 byte

• double – 8 byte

• bool – 1 byte (only in C++)


More on Variables

• Declaration – – int number1;– float number2;

• Initialization –– int number1 = 0;– int number2 = 3.3;

• Assignment-– number1=5;– number2=number1;


Variable Scope

• Global Variables – variables that are declared above main() can be accessed anywhere after the declaration

• Local Variables – variables declared in section of code {}. Only accessible in that region.


Characters and Strings

• ‘a’ is a character• “sfsddsfsf” is a string• In C and C++ a string a char[]

char name[]=“Omar”;printf(“My name is %s\n”, name);

• \n is used for newline• %s shows that a parameter for printf is a

string


Characters and Strings in C

• Converting a char to an intInt a;

A=atoi(“45”);

• Similar function atof() for floating point.

• Reading input from keyboard with scanf()char string1[20];

printf(“Enter a string:\n”);

scanf(“%s, string1);


Copying Strings

• Copy entire string using strcpy()char a[] = “Computer”;

char b[25];

strcpy(b,a);

• Copy part of string using strncpy()strncpy(b,a,4);

b[4] =‘\0’;

• ‘\0’ is used as NULL character

• Strcar() and Strncat() to append strings.


Comparing Strings

• See if 2 strings are the same with strcmp()– Strcmp(s1,s2)– Returns 1 if equal

• Compare part of strings using strncmp()


Formatting Output

• Inside of printf(“ ”); you can use escape characters like \n;– \t move to tab– \r carriage return– \f move cursor to next page

• These are called escape sequences


Formatting Input

• In scanf(“ “, variablename); we can specify the type of input like %s;– %d or %I for integer– %c char– %s char array or string

• These are called conversion specifiers


Constants

• #define PI 3.14159265

• The preprocessor reads any line that begins with a #.

• Declaring a constant– Const zero 0;


Arithmetic Operators

• + addition

• - subraction

• * multiplication

• / division

• % modulo or remainder

• As in javaa = --b;

a = b++;

a++;


Relation Operators

• == Equal

• != Different

• > Greater than

• < Less than

• >= Greater or equal than

• <= Less or equal than

• Relation Operators return type bool (true or false) in C++

• In C they return an int; 1 for true and 0 for false;


C++ I/O

• C++ has a different way of hanlding input and output, using the iostream C++ library

cout << “Omar”;

cout << Omar << lastname << “ is me\n”;

• Input using cinint number;

cin >> number;

cout << number << endl;


Control structures

• if (cond) state1 else if (cond2) state2 else state3• while (expression) statement• do statement while (cond)• for (init; cond; increment) statement;

• Use break, continue and goto to jump around the code.


Switch Statement

switch (x) { \

case 1:

cout << "x is 1";

break;

case 2:

cout << "x is 2";

break;

default:

cout << "value of x unknown";

}


Functions

• We can use functions to achieve structured programmingInt add(int a, int b){

a = a+b; return (a);

}

• ‘int’ is the return type, ‘a’ and ‘b’ are arguments• When we call the function we must pass it

parameters matching the arguments


Passing Parameters

• Call By Value– This is what we usually do, we pass a function

the value of a variable

• Call By Reference– Instead of the value we will pass a pointer to

the variable. If we modify the passed variable the change will be seen by the caller

– We use ‘&parm’ to show that we are passing the variable at the memory location of parm


Arrays

• Intialization– int numbers[5]={0,1,2,3,4,};

• Accessing– num2 =numbers[1];– numbers[0]=99;

• Passing arrays as parameters– Declaration: int add(int numarray[])– Call:

int array[]={1,2,3};add(array);


Pointers

• We used pointers in call by reference

• Valuable in implementing data structures

• Referencing– by a variable name is called a direct

reference.– Through a pointer is called indirection (*)


Indirect Referencing

int number=5;

int *numberPtr;

• Number directly referencing a variable whose value is 5;

• numberPtr indirectly referencing the value.• Initialize pointers when they are declared.


Address Operator

• The ‘&’ operator returns the ‘address of’ its operand.

int num=5;

int* numPtr;

numPtr = &y;

• So numPtr set to the address of y;


More on Pointers

• The two operators & and * are complements• Given:

Int num;Int *numPtr;numPtr =&num

• Then:– &*numPtr is same as &*numPtr;– The value of num can be accessed using ‘num’ or

‘numPtr’– The address of num can be accessed using ‘&num’ or

‘numPtr’– Conversion specifier for pointers is ‘%p’


Sizeof()

• The Sizeof() function is used to determine how many bytes of a data type during compilation.

• Ex:sizeof(float) equals 4

float array[10];

sizeof(array) equals 4*10 which is40


Dynamic Memory

• Dynamic Memory allows us to determine and allocate memory to variables and data structures at ‘run time’.

• C++ uses new and delete;– pointer = new type;

• New returns a pointer to the allocated memory

– delete pointer;• Frees up the memory that was allocated


Dynamic Memory in C

• C does not use new and delete• It uses malloc(), free(), etc… found in

stdlib.h ANSI C library• pointer = (type cast) malloc(nbytes);

Int* numPtrnumPtr =(int*) malloc(sizeof(int));

• free(pointer) releases the allocated memory


Structs

• Similar to records in Ada.struct person_t{

char fname[20];char lname[20];int age;

}person1, person2;

• Here we are declaring person1 and person2 as type person_t.

• By convention we use the _t


Accessing the struct members

• We use the ‘.’ to access members of a structcout << person1.fname;

person1.fname=“John”;


What about Pointers to Structs

• We can point to a struct like other structures.Person_t* person1Ptr;

person1Ptr = &person1;

• We can no longer use the ‘.’ to access the members in the struct we are pointing to.– The ‘->’ is used

Cout << person1Ptr->fname;

– Element fname of structed pointed by person1Ptr

– Same as *(person1Ptr.fname);


Other Types

• Defining your own types can be done using typdef– Typedef existing_type new_type;

• Unions allow the same portion of memory to be accessed as different data types;

• Enum is like Enumeration Types in Ada– When you grouped the months or days together


C++ Classes

• C++, not C, has the ablity to create classes which is similar to Java, using class

• Classes can contain data and functions

• Members of the class can be private, protected or public.– Protected members are only accessible by

friend classes.


Class Example from cplusplus.com

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

};CRectangle::CRectangle (int a, int b) {

width = a; height = b; }

int main () { CRectangle rect (3,4); CRectangle rectb (5,6); cout << "rect area: " << rect.area() << endl; cout << "rectb area: " << rectb.area() << endl; }


More on Classes

• Destruct is automatically called if it is definedCRectangle::~CRectangle () { delete width; delete height; }

• You can overload constructers, each with diff parameters. – When you declare a new class instance,

using a constructor with no parameters then don’t use parethesis.• MyClass aclass;


Little More on C++

• C++ allows for operator overloading• Unlike Java, C++ allows for multiple

inheritance. – A child can have 2 parents

• The keyword this works like it does in Java

• Templates, Namespaces, Friend later in the semister.


Header Files

• .h files are strictly convention,• Anything in these files can be put in .c

or .cpp files• Usually in the header file we put variable

definition,library includes, function prototype(its sign), constants, typdefs.

• Header files separate implementation for interface like (.ads and .adb in Ada)


C Concepts

• Scope is basically top down

• Everything in C is a function

• Relies heavily on programmers’ conventions

• Physical modularity through the file and logical through the functions.


C++ Concepts

• Proper subset of C

• Classes allow for large scale programming and encapsulation.

• Templates support generic programming

• Class is unit of logical modularity.

C/C++ Programming on Hobbes(Unix) Omar Haque Csci 169 Spring 2003.

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