Introduction to c

1. JustETC Education Inc.

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

3.  How does a C program look like?
#include <stdio.h>
main()
{
printf("hello, worldn");
}

4.  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

6.  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.  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.  printf(“%st%s”, “Hello”, “World”);
 printf(“%dt%f”, 100, 200.50);

9.  Variables:
◦ Example: x, y, z
◦ x=10, y=100.5
◦ printf(“%dt%f”,x,y);
◦ word=“Hello World”;
◦ printf(“%s”,word);
 More correctly
◦ int x = 10, float y=100.5;
◦ char x[50] = “Hello World”;
◦ int intArr[5] = {1,2,3,4,5};

10.  Note:
◦ t, b, n
◦ t: print a tab
◦ n: print a newline

11.  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.  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. if (expression)
statement1
else
statement2
----
if (expression)
statement1
else if (expression)
statement2
else
statement3

14. 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 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(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 (expression) {
case const-expr: statements
case const-expr: statements
default: statements
}

18.  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. while (expression){
Statement
}
for (expr1; expr2; expr3){
Statement
}
expr1;
while (expr2) {
statement
expr3;
}

20.  For
◦ int n=100,i=0;
◦ for (i = 0; i < n; i++){
 printf(”%dn”,i);
◦ }
 While
◦ int n=100,i=0;
◦ while(i <n){
 printf(”%dn”,i);
 i++;
◦ }

21.  Do-While
◦ int n=100,i=0;
◦ do {
 printf(”%dn”,i);
 i++;
◦ } while(i <n);

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

23.  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.  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.  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.  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.  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.  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.  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.  Example:
◦ int a[10][20];
◦ int *a[10];
◦ char name[][50] = { "Illegal month", "Jan", "Feb",
"Mar" };
◦ char *name[] = { "Illegal month", "Jan", "Feb", "Mar"
};

31.  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
◦ & 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.  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.  int getchar(void)
 int putchar(int)
 int printf(char *format, arg1, arg2, ...);
 printf("%.*s", max, s);
 int scanf(char *format, ...) : Read from user/console
 int sscanf(char *string, char *format, arg1, arg2, ...): from
string

35.  FILE *fp;
 FILE *fopen(char *name, char *mode);
 int fclose(FILE *fp)
 char *fgets(char *line, int maxline, FILE *fp)
 int fputs(char *line, FILE *fp)

36.  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.  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.  struct student {
◦ int id;
◦ 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.  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.  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.  struct student 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.  struct student{
◦ int id;
◦ char *name;
◦ char *address;
◦ char *cell;
} studentList = {
{100,”name1”,”address1”},
{101,”name2”,”address2”},
{102,”name3”,”address3”}
 };

43.  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 tag {
◦ int ival;
◦ float fval;
◦ char *sval;
 } u;

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

46.  Misc
◦ int ungetc(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.  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.  “The C Programming Language”: Kernighan
and Ritchie
 Internet