Values & Variables 1

Transcription

1 Values & Variables 1

2 Properties of variables Should have a type Stores data Case sensitive Their names can not start with a number Reserved keywords can not be used as variable names 2

3 Keywords 3

4 How to define a variable Type Value int x = 3; Variable Semicolon: End of statement 4

5 Ways to define a variable int ninteger; string sstring; int ninteger = 42; string sstring = "This is a string!"; int ninteger; string sstring;... ninteger = 42; Double quotes represents a string sstring = "This is a string!"; 5

6 Necessity to set a value to a variable string svalueless; MessageBox.Show(sValueless); Error! 6

7 Variable Types Simple types Integers Floating point numbers Characters Strings 7

8 Integers short 2 bytes ( 32,768 <-> 32,767) short sval = -12; ushort 2 bytes (0 <-> 65,535) ushort sval= 12; int 4 bytes ( 2,147,483,647 <-> 2,147,483,647) int nval = ; uint 4 bytes (0 <-> 4,294,967,295) uint nval = 12500; long 8 bytes long lval = ; ulong 8 bytes Ulong lval =

9 Floating Point Numbers float 4 bytes float fval = -1,2; double 8 bytes double dval = ; decimal 8 bytes decimal dval = ; 9

10 Expressions Expressions are used for performing operations over variables. Return a value of known type. Two types of expressions Operators Functions 10

11 Arithmetic operations They need more than one variable. Performs mathematical operations + (addition operation) - (subtraction operation) * (multiplication operation) / (division operation) % (modulus operation). 11

12 Arithmetic operations Abbreviations int m = 5; int n = 4; m = m + n; equals m += n; In other words in the end of both expressions m will have value of 9 and the value of n will not be changed. 12

13 Increment and decrement operations They operate on one variable ++ is increment operator i++; i = i + 1; -- is decrement operator i --; i = i 1; Prefix and postfix operators will yield to different results. i.e. i++ and ++i are not same. 13

14 Increment and decrement operations ++k The result of the operation is the value of the operand after it has been incremented. k++ The result of the operation is the value of the operand before it has been incremented. --k The result of the operation is the value of the operand after it has been decremented. k-- The result of the operation is the value of the operand before it has been decremented. 14

15 Example int k=0, m; Values of m and k will be 1 m = ++k; int k=0, m; m = k++; m will be 0 and k will be 1 int k=5, m, n=2; m = --k + n; m will be 6 and k will be 4 int k=0, m, n=7; m = k n; m will be 6 and k will be 1 and n will be 6 15

16 Exercise What will be the values of the variables after code piece below is executed? int i, j, k; i = 2; j = 3 + i++; k = i; i *= ++k + j--; i /= k j; 16

17 Exercise Assuming that line of codes are independent, what will be the value of variable m after each line is executed? int i = 0, j = 6, k = 4, m = 5; m = k i; m *= j % 4; m += k++ + (j-- * ++i); 17

18 Order of Operations Rules that defines which procedures should be performed first. In C# language some operators have execution privilege over others. To predict the result of an expression first we should know the order of operations. 18

19 Example PEMDAS phrase may help to remember the order * 3-4 / 5 =? 1 + (2 * 3) (4 / 5) P E M D A S Parenthesis Exponent Multiplication Division Addition Subtraction

20 Example(result) If we use all numbers in integer type then the result will be integer(in other words fraction will be removed) 1 + (2 * 3) (4 / 5) 7 4/5 = 0 (integer division) 20

21 Exercise Different data types may yield different results in same operations. Write and execute the codes in the next slides. Explain the difference between results. 21

22 Exercise (continues) 22

23 Exercise (continues) 23

24 Characters char 1 byte 'a' 'z' 'A' 'Z' '?' '@' '0' '9' Special characters are represented by using \ prefix. '\n' : new line '\t' : tab '\'' : single quote '\\' : backslash 24

25 Strings (Character Arrays) Sequence of characters. Example: Hello! first line\n second line \n third line Empty string 25

26 Strings string Class Unicode 16 bit Example: string mystring = Hello! ; Verbatim strings string mystring 2.5 disk ; 26

27 string operations Appending two strings Result: Hello world! 27

28 string operations Searching within a string int IndexOf () Result: 1 Exercise: Find the usage of LastIndexOf() function and write an example by using this function. 28

29 string operations Retrieve a substring from a string string Substring() Result : llo 29

30 Exercise Put your name and surname into two string variables. Concatenate two strings. Write the result to the console. 30

31 DateTime C# language has built-in DateTime structure to represent date and time values. We can store year, month, day, hour, minute, second values in a DateTime structure. 31

32 Creating a DateTime Object Type Creating a new object DateTime dt = new DateTime(year, month, day); Variable name Initial values 32

33 Example A new DateTime object is created 33

34 Constants Their values can not be changed. They have types. We can use them in expressions bur can not alter them. Defined by using const keyword before variable type. Their values can be set only during definition line. const int nvar = 34; 34

35 Example 35

36 Advanced Computer Programming HOMEWORK HW1: Install VS.Net 2015 HW2: Write a program to display user s complete mailing address. Accept user s name, city, street, pin and house no. HW3: Write a program to display student information. Accept Student s name, Roll no, Age, class, and university name and display it on console. 36