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C/C++ Programming on Hobbes(Unix)

C/C++ Programming on Hobbes(Unix). Omar Haque Csci 169 Spring 2003. TA Information . Name: Omar Haque Email: ohaque@gwu.edu Office Phone: not ready Office Room: not ready Office Hours: Tuesday 1pm –3pm. Open Lab. Tuesday Han Young will run the lab I will be there to help out

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C/C++ Programming on Hobbes(Unix)

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

  2. TA Information • Name: Omar Haque • Email: ohaque@gwu.edu • Office Phone: not ready • Office Room: not ready • Office Hours: Tuesday 1pm –3pm Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

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

  4. ANSI • American National Standards Institute • 1990 approved standard for C • 1997 approved standard for C++ Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

  5. 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; } Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

  6. Compiling and Execute C Program • % gcc filename.c –o outputfile • GNU C compiler • Preprocess, compile, link • % ./outputfile Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

  7. 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; } Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

  8. Compile and Execute C++ • % CC hello.cpp –o outputfile • Sun C++ compiler • % g++ hello.cpp –o outputfile • GNU C++ compiler • % ./outputfile Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

  9. Comments • C requires comments to be delimited by /* and */ • C++ allows // for one line comments • C++ also allows /* */ Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

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

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

  12. More on Variables • Declaration – • int number1; • float number2; • Initialization – • int number1 = 0; • int number2 = 3.3; • Assignment- • number1=5; • number2=number1; Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

  13. Variable Scope • Global Variables – variables that are declared above main() can be accessed anywhere after the declaration • LocalVariables – variables declared in section of code {}. Only accessible in that region. Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

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

  15. Characters and Strings in C • Converting a char to an int Int 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); Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

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

  17. Comparing Strings • See if 2 strings are the same with strcmp() • Strcmp(s1,s2) • Returns 1 if equal • Compare part of strings using strncmp() Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

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

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

  20. Constants • #define PI 3.14159265 • The preprocessor reads any line that begins with a #. • Declaring a constant • Const zero 0; Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

  21. Arithmetic Operators • + addition • - subraction • * multiplication • / division • % modulo or remainder • As in java a = --b; a = b++; a++; Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

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

  23. 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 cin int number; cin >> number; cout << number << endl; Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

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

  25. Switch Statement switch (x) { \ case 1: cout << "x is 1"; break; case 2: cout << "x is 2"; break; default: cout << "value of x unknown"; } Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

  26. Functions • We can use functions to achieve structured programming Int 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 Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

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

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

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

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

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

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

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

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

  35. 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*numPtr numPtr =(int*) malloc(sizeof(int)); • free(pointer) releases the allocated memory Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

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

  37. Accessing the struct members • We use the ‘.’ to access members of a struct cout << person1.fname; person1.fname=“John”; Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

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

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

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

  41. 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; } Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

  42. More on Classes • Destruct is automatically called if it is defined CRectangle::~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; Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

  43. Little More on C++ • C++ allows for operator overloading • Unlike Java, C++ allows for multiple inheritance. • A child can have 2 parents • The keyword thisworks like it does in Java • Templates, Namespaces, Friend later in the semister. Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

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

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

  46. C++ Concepts • Proper subset of C • Classes allow for large scale programming and encapsulation. • Templates support generic programming • Class is unit of logical modularity. Omar Haque | C/C++ on Hobbes (Unix) | Csci169 | Spring 2003

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