Advanced Computer Programming

Transcription

1 Hazırlayan Yard. Doç. Dr. Mehmet Fidan

2 VARIABLE TYPES Integral Types: In C#, an integral is a category of types. For anyone confused because the word Integral sounds like a mathematical term, from the perspective of C# programming, these are actually defined as Integral types in the C# programming language specification. They are whole numbers, either signed or unsigned, and the char type. The char type is a Unicode character, as defined by the Unicode Standard. For more information, visit The Unicode Home Page. Type Size (in bits) Range sbyte to 127 byte 8 0 to 255 short to ushort 16 0 to int to uint 32 0 to long to ulong 64 0 to char 16 0 to 65535

3 VARIABLE TYPES Floating Point and Decimal Types: A C# floating point type is either a float or double. They are used any time you need to represent a real number, as defined by IEEE 754. For more information on IEEE 754, visit the IEEE Web Site. Decimal types should be used when representing financial or money values. Type Size (in bits) precision Range float 32 7 digits 1.5 x to 3.4 x double digits 5.0 x to 1.7 x decimal decimal places 1.0 x to 7.9 x float 4 bytes float fval = -1,2; double 8 bytes double dval = ; decimal 8 bytes decimal dval = ;

4 VARIABLE TYPES The String Type: A string is a sequence of text characters. You typically create a string with a string literal, enclosed in quotes: "This is an example of a string. string mystring = Hello! ; Hello! Verbatim strings string mystring 2.5 disk ; string e = "Joe said \"Hello\" to me"; string f said ""Hello"" to me"; string g = "\\\\server\\share\\file.txt"; string h 2.5 disk Joe said "Hello" to me Joe said "Hello" to me \\server\share\file.txt \\server\share\file.txt Some characters aren't printable, but you still need to use them in strings. Therefore, C# has a special syntax where characters can be escaped to represent non-printable characters. For example, it is common to use newlines in text, which is represented by the '\n' char. The backslash, '\', represents the escape. When preceded by the escape character, the 'n' is no longer interpreted as an alphabetical character, but now represents a newline. You may be now wondering how you could represent a backslash character in your code. We have to escape that too by typing two backslashes, as in '\\'.

5 TYPE CONVERSION Value must be compatible with the variable. If not, we have to make a type conversion. Some data types can be converted to an other and some can not. We can lose data during unsafe conversion e.g. assigning a floating point number to an integer. In that case we lose fraction. Implicit Conversion Explicit Conversion

6 IMPLICIT CONVERSION Numeric Numeric Properties: Occurs between compatible types. Transfers data from a smaller type to a bigger type. No data loss. No extra operation. Automatic type conversion.

7 IMPLICIT CONVERSION Type float 32 double 64 decimal 128 Size (in bits) Type Size (in bits) Range sbyte 8 byte 8 short 16 ushort 16 int 32 uint 32 long 64 ulong 64 char 16

8 IMPLICIT CONVERSION Implicit Conversion No data loss

9 EXPLICIT CONVERSION Numeric Character Character Numeric Occurs between incompatible types. May lose data. Extra coding needed. Use with caution.

10 EXPLICIT CONVERSION Type Size (in bits) Range sbyte to 127 byte 8 0 to 255 short to ushort 16 0 to int to uint 32 0 to long to ulong 64 0 to char 16 0 to 65535

11 .ToString() method. NUMERIC TO CHARACTER Can be used with numeric types. Converts numeric value to string type. There is also a formatting option.

12 NUMERIC TO CHARACTER Output : 123

13 FORMATTING EXAMPLE NumberFormatInfo class. Used especially with floating point numbers. Resides under System.Globalization namespace. Formatting properties Number decimal digits Number decimal separator Number group separator

14 FORMATTING EXAMPLE Output: ,67 Detailed Information:

15 CHARACTER TO NUMERIC Convert class Explicit Conversion Used in conversion of multiple types. There should be compatible types between conversions. Output: 132

16 CHARACTER TO NUMERIC

17 CHARACTER TO NUMERIC Console.ReadLine() class Used for getting input from screen. String type value is returned. Returns when user press Enter key. Later, return value can be converted to other types.

18 LOGICAL OPERATORS and CONTROL STATEMENTS Boolean Boolean takes true or false values. Used in deciding states. Commonly used in conditional statements and loops. A logical operation is a formula that has a true or false result. Boolean variables are defined with bool keyword. bool bval = true;

19 BOOLEN EXAMPLE

20 BOOLEN OPERATORS Used for constructing Boolean expressions. and && or not! equal == Not equal!= Comparison <, >, <=, >=

21 AND (&&) OR ( ) NOT (!) AND: Both values must be true. OR: At least one value is to be true. true && true = true false && true = false true && false = false false && false = false true true = true false true = true true false = true false false = false NOT: Reverses the value.!true = false!false = true

22 EQUAL (==) NOT EQUAL (!=) COMPARISON EQUAL: Returns true if two values are equal. NOT EQUAL: Returns true if two values are not equal. 1 == 2 1 == 0 42 == 42 variable1 == othervariable 1!= 2 1!= 0 42!= 42 a!= variable COMPARISON: (>,<,>=,<=): 1 < 2 0 > 1 42 <= 42 age>= 18

23 OPERATOR PRIORITY Highest Parantheses Not (!) Comparison(<, >, <=, >=) Equals(==) Not Equals(!=) And(&&) Or( ) Lowest

24 EXAMPLE

25 EXAMPLE Parantheses Not (!) Comparison(<, >, <=, >=) Equals(==) Not Equals(!=) And(&&) Or( )

26 CONTROL STATEMENTS: IF - ELSE Decides which code block will run depending on the result of logical expression. Logical expressions retuns boolean values. If return value is true then code blocks within th if statement will be executed. Otherwise else statement will be executed. A simple if case decides whether corresponding code block will be executed or not. A structure that is composed of if and else will execute two different code blocks depending on the logical expression. if/else statement can be used in nested forms to express more complex stuations.

27 If control statements has two forms: IF CASE } if ( expression ) { codes; or if ( expression ) code;

28 IF CASE Common if use case : if ( expression ) statement; We can also write if else as: if (expression ) statement1; else statement2;

29 IF CASE if ( boolean expression is true ) statement ; else if (boolean expression is true) statement ; else statement ;

30 IF CASE When there are multiple conditions with one line of statements, we can use if-else structure seen below: if (boolean expression is true ) statement; else if (boolean expression is true ) statement; else if (boolean expression is true ) statement; else statement;

31 IF CASE if (boolean expression is true ) { statement blocks; } else if (boolean expression is true ) { statement blocks; } else { statement blocks; }

32 IF CASE

33 EXERCISE Meteorogy department asks for a program that converts humudity values to a human readable format. Program will write to output the following results depending input ranges between 0 and 100. %20 and lower too dry" %21 - %40: dry" %41 - %60: little dry" %61 - %80: little moist" %81 and higher: moist Write a program that takes a humudiy value from user and writes it s corresponding human readable output.

34 SWITCH CASE Used if the value of a variable is used for controlling the program flow. May execute different code blocks for each different value of the variable. C# language offers this functionality with switch-case structure.

35 switch (variable ) { case constant_value1 : statements; break; case constant_value2 : statements; break; case constant_value3 : statements; break; default : statements; break; } SWITCH CASE switch is the starting point of the structre. A variable should be provided after switch. This variable could be numeric or character. We should use only constant value in case sections, no expressions. All cases should end with break keywords. No need to use { } paranthesis aftes cases.

36 SWITCH CASE Write a program that takes the course grade (just one letter) from user. Your program will write the following result to the output depending on the grade. A: best" B: good" C: all right" D: not bad" F: bad"

37 SWITCH CASE

38 EXERCISE Meteorogy department asks for a program that converts humudity values to a human readable format. Program will write to output the following results depending input ranges between 0 and 100. %20 and lower too dry" %21 - %40: dry" %41 - %60: little dry" %61 - %80: little moist" %81 and higher: moist Write a program that takes a humudiy value from user and writes it s corresponding human readable output by using switch /case control structure.

39 switch (variable ) { case constant_value1 : statements; break; case constant_value2 : statements; break; case constant_value3 : statements; break; default : statements; break; } SWITCH CASE NOTES double and decimal types are not used within switch paranthesis. Any number of statements can be used within the case element. Using default: element help us to detect defects. Forgetting to use breaks is the most common coding bad habbit. Check for breaks after constructing the switch structure.

40 EXAMPLES You enter a character from the keyboard, and the program uses a nested if statement to determine whether the input character is an alphabetic character. If the input character is an alphabetic character, the program checks whether the input character is lowercase or uppercase. A message appears for each case. Console.Write("Enter a character: "); char c = Convert.ToChar(Console.ReadLine()); if (Char.IsLetter(c)) { if (Char.IsLower(c)) { Console.WriteLine("The character is lowercase."); } else { Console.WriteLine("The character is uppercase."); } } else { Console.WriteLine("The character isn't an alphabetic character."); }