Introduction to C Programming Language by Mr. S. Ahmed

1. Introduction to CProgramming Languageby Mr. S. Ahmed JustETC Education Inc.

2. Topics/Concepts • Structure of C Program • Data Types, Operators, and Expressions • Control Flow • Functions and Program Structure • Pointers and Arrays • Structures • Input and Output

3. Structure of a C Program • How does a C program look like? #include <stdio.h> main() { printf("hello, world\n"); }

4. The ‘Hello World’ Program • What it does? • Displays/prints/echos ‘hello World’ • What do the different sections indicate? • Header Files • Code Blocks, functions • Statements • How to compile • Depends on the Operating System and IDE you use • How to Run? • Depends on the Operating System and IDE you use

5. Program Structure Program Structure

6. Program Execution, Program in Action • How to compile • Depends on the Operating System and IDE you use • Save the file as hello.c • Linux/Unix: cc hello.c • How to Run? • Depends on the Operating System and IDE you use • Linux/Unix: a.out • Windows: • Usually you will use an IDE • IDE will have menu options to compile and run • Commons are: f9, shift+f9, f5 are used to compile/run. • Menus may have options such as compile, build, run, debug, build all, auto build

7. Remember • A program is nothing but a set of instructions to the computer hardware to perform some operations. • Each line of instructions is called a statement • A semicolon is placed at the end of each statement • You can group a set of instructions by placing them in between { } • You can assign a name to a code block inside { } – then the code block is called function/procedure/method • You can define your own functions (code blocks) • C also have many functions/code blocks already defined • Hence, a program will consist some blocks of instructions defined by you, or will use instruction block as defined by C itself • Remember, one function can call /use another function • As a statement • While calling another function, some information can be passed to the other function – called Arguments

8. Some Variations of the Printf() Function • printf(“%s\t%s”, “Hello”, “World”); • printf(“%d\t%f”, 100, 200.50);

9. Concepts to Understand • Variables: • Example: x, y, z • x=10, y=100.5 • printf(“%d\t%f”,x,y); • word=“Hello World”; • printf(“%s”,word); • More correctly • int x = 10, float y=100.5; • char x[50] = “Hello World”; • intintArr[5] = {1,2,3,4,5};

10. Concepts to Understand • Note: • \t, \b, \n • \t: print a tab • \n: print a newline

11. Variable and Expressions • Understanding by Examples • int x=10, y=20, sum=0; • sum = x + y; sum = (x + y); (you can think (x+y) as an expression) • (x>y) is an expression • ((x+y) > 20) is an expression • An expression is a statement that has a value. In C, C++ and C#,an expression is always inside brackets like these examples. [about.com] • ( y > 4) • ( x== 8) • ( c = 1)

12. Control Flow. What is it? • Write a program that will print 1 if today is holiday else it will print 0. • If today is holiday printf(“%d”,1); • else if today is not holiday printf(“0”); • Controlling what the program will do • Control the flow of the instruction block • Which instruction will do something • Which instruction will sit idle • Decide if the same statements will run 100 times or not

13. Control Flow if (expression) statement1 else statement2 ---- if (expression) statement1 else if (expression) statement2 else statement3

14. If then Else if (a > b) z = a; else z = b; ---- if (a > b) z = a; else if (b>a) z = b; else if (a==b) x=y; else printf(“nothing”);

15. Switch-Case • Switch-case can be used instead of if then else sometimes (not always). • If (1==a) • statement1 • else if (2==a) • Statement2 • else if (3==a) • Statement3 • else • statement4

16. Switch-Case Equivalent of If switch(a){ • Case 1:statement1;break; • Case 2:statement2;break; • Case 3:statement3;break; • default:statement4;break; } • Fall through: break is required to stop the flow otherwise it will keep running until it sees a break. • Default: When no match is found.

17. Switch switch (expression) { case const-expr: statements case const-expr: statements default: statements }

18. Loop • Execute a set of instructions over and over • For specific number of times • As long as an expression is true/satisfied • For Loop • Specific number of times • While, and Do-While • As long as an expression is true/satisfied

19. Loops Syntax while (expression){ Statement } for (expr1; expr2; expr3){ Statement } expr1; while (expr2) { statement expr3; }

20. Loops Example • For • int n=100,i=0; • for (i = 0; i < n; i++){ • printf(”%d\n”,i); • } • While • int n=100,i=0; • while(i <n){ • printf(”%d\n”,i); • i++; • }

21. Loop Example • Do-While • int n=100,i=0; • do { • printf(”%d\n”,i); • i++; • } while(i <n);

22. Break and Continue • Break • Get out of the current loop • Continue • Stop executing current iteration and go to next iteration

23. Go to Statement • Syntax • Go to Label • …… • ……… • Label: • ……. • Operation • Jump to the labeled place from current place • Not encouraged • Rarely can be used to get out of deeply nested loops.

24. Pointers • What are Pointers? • Note: pointers usually lead to more compact and efficient code • A pointer is a variable that contains the address of another variable • If p is a pointer and c is a variable the statement • p = &c; • assigns the address of c to the variable p. & gives the address of a variable

25. Pointers • The & operator only applies to objects in memory: variables and array elements. • Pointers cannot be applied to expressions, constants, or register variables • when * is applied to a pointer, it accesses the object the pointer points to

26. Pointers • Examples • int x = 1, y = 2, z[10]; • int *ip; /* ip is a pointer to int */ • ip = &x; /* ip now points to x */ • y = *ip; /* y is now 1 */ • *ip = 0; /* x is now 0 */ • ip = &z[0]; /* ip now points to z[0] */

27. Pointers • Every pointer points to a specific data type • one exception: • a ``pointer to void'‘ (void *p) is used to hold any type of pointer • You cannot use dereference with void * • If p points to the integer x, then *ip can occur in any context where x could • *ip = *ip + 10; • y = *ip + 1 • ++*ip • (*ip)++

28. Pointers as Function Parameters • Call by reference applies here void swap(int *px, int *py) /* interchange *px and *py */ { int temp; temp = *px; *px = *py; *py = temp; } main() { swap(x, y); //The values of x and y will also get changed here }

29. Pointers and Arrays • Any operation that can be achieved by array subscripting can also be done with pointers • int a[10]; int *pa; pa = &a[0]; • x = *pa; is equivalent to x=a[0]; • pa+1 points to the next element pointed by pa • pa+i points i elements after pa • and pa-i points i elements before • Thus, if pa points to a[0] • *(pa+1) refers to the contents of a[1], • pa+i is the address of a[i], and • *(pa+i) is the contents of a[i]

30. Pointers and Multi-dimensional Arrays • Example: • int a[10][20]; • int*a[10]; • char name[][50] = { "Illegal month", "Jan", "Feb", "Mar" }; • char *name[] = { "Illegal month", "Jan", "Feb", "Mar" };

31. Bitwise Operators • Applies only to char, short, int, and long whether signed or unsigned • & bitwise AND • | bitwise inclusive OR • ^ bitwise exclusive OR • << left shift • >> right shift • ~ one's complement (unary) (alternate bits)

32. Bitwise Operators • Bitwise Operators • & can be used to turn off some bits • x= x & 031, turn off (0) all bits except last five • | is used to turn bits on (1) • ^ sets • a one in each bit position where its operands have different bits, and • zero where they are the same. • << and >> perform left and right shifts of their left operand • x >> 2; y << 2;

33. Left and Right Shifts • x << 2 • shifts the value of x by two positions • fills vacated rightmost bits with zero • One left shift multiplies the number by 2 • Right shifting (Signed Number): The vacated left most bits • will be filled with bit signs on some machines – arithmetic shift • and with 0-bits on others - logical shift

34. I/O Functions • intgetchar(void) • intputchar(int) • intprintf(char *format, arg1, arg2, ...); • printf("%.*s", max, s); • intscanf(char *format, ...) : Read from user/console • intsscanf(char *string, char *format, arg1, arg2, ...): from string

35. File Operations • FILE *fp; • FILE *fopen(char *name, char *mode); • intfclose(FILE *fp) • char *fgets(char *line, intmaxline, FILE *fp) • intfputs(char *line, FILE *fp)

36. Common I/O Functions • String related functions as defined in string.h • strcat(s,t) concatenate t to end of s • strncat(s,t,n) concatenate n characters of t to end of s • strcmp(s,t) return negative, zero, or positive for s < t, s == t, s > t • strncmp(s,t,n) same as strcmp but only in first n characters • strcpy(s,t) copy t to s • strncpy(s,t,n) copy at most n characters of t to s • strlen(s) return length of s • strchr(s,c) return pointer to first c in s, or NULL if not present • strrchr(s,c) return pointer to last c in s, or NULL if not present

37. Structures • What is a structure? • It is just a data type/variable that has multiple variables under it • Why do we need it? • For example, you are writing a student record management system. Now to define a student in your software, you have to keep many variables. Such as id, name, address, phone, email, major, minor, and some more. • Yes, you can deal with all these variables for all students • Better if you had only one variable for each student but as we see many variables are required to represent a student • So why not create one variable for a student and put the other variables under that [to represent that particular student) • The top level variable is the structure type

38. Defining Structures • structstudent { • intid; • char *name; • char * address; • char *cell; • }; • Struct defines a data type. Hence, student now is a data type. We can define variables of student type as follows • student studentVar;

39. Defining Structures • We can declare and assign at the same time • student studentVar = {100,”smith” ,”winnipeg”,”999-0539”}; • We can assign separately as well • student studentVar; • studentVar.id=100; • studentVar.name=“smith”;

40. Structures • How to print structure variable data? • printf("%d,%s", studentVar.id, studentVar.name); • Legal operations with structures • Copy it as a unit • Assign to it as a unit • Take it’s address with & • Access it’s members

41. Pointers to Structures • structstudent studentVar, *pp; • pp = &studentVar; • printf(“student details (%d,%s)\n", (*pp).id, (*pp).name); • printf(“student details (%d,%s)\n", pp->id, pp->name); • Notice the above two lines. How the member variables were accessed. • (*pp).id or pp->id

42. Array of Structures • structstudent{ • int id; • char *name; • char *address; • char *cell; } studentList = { {100,”name1”,”address1”}, {101,”name2”,”address2”}, {102,”name3”,”address3”} • };

43. Union • Union declaration, assignment may look like pretty similar to structures • Unions are usually used to store data of different data types for the same concept • All member variables points to the same memory location • Actually, we are trying to store one value • But as the data type of the value can differ, hence, we are keeping options • Usually, the storage will be of the size of the largest data type • The programmer is responsible to remember and extract the same data type he stored • For example, you want to store tags. However, tags can be of int, float, or string type based on context. Then you can declare a union as follows

44. Union • union tag { • intival; • float fval; • char *sval; • } u;

45. Enum • enum DAY { saturday, sunday , monday, tuesday, wednesday, thursday, friday } workday; • enum DAY today = wednesday;

46. I/O Functions • Misc • intungetc(int c, FILE *fp) • system("date"); • Storage Management • void *malloc(size_t n) • void *calloc(size_t n, size_t size) • int *ip; • ip = (int *) calloc(n, sizeof(int));

47. I/O Functions • Mathematical Functions • sin(x) x in radian • cos(x) • atan2(y,x) • exp(x) • log(x) (x>0) , natural • log10(x) (x>0) , 10 based • pow(x,y) x to the power y • sqrt(x) • fabs(x) absolute value of x

48. References • “The C Programming Language”: Kernighan and Ritchie • Internet