Chapter 4: How to Work with Numeric and String Data

Transcription

1 CIS 260 C# Chapter 4: How to Work with Numeric and String Data 1. Built-in Values C#.NET keyword Bytes type Description byte 1 Byte Positive integer value from 0 to 255 sbyte 1 SByte Signed integer value from -128 to 127 short 2 Int16 Integer from 32,768 to +32,767 ushort 2 UInt16 Unsigned integer from 0 to 65,535 int 4 Int32 Integer from 2,147,483,648 to +2,147,483,647 uint 4 UInt32 Unsigned integer from 0 to 4,294,967,295 long 8 Int64 Integer from 9,223,372,036,854,775,808 to +9,223,372,036,854,775,807 ulong 8 UInt64 Unsigned integer from 0 to +18,446,744,073,709,551,615 float 4 Single Non-integer number with approximately 7 significant digits double 8 Double Non-integer number with approximately 14 significant digits decimal 16 Decimal Non-integer number with up to 28 significant digits (integer and fraction) that can represent values up to 79,228 x 1024 char 2 Char A single Unicode character bool 1 Boolean A true or false value 2. Declaration and Initialization of Variables A variable is a name of memory location which stores a value that can change as a program executes Naming conventions: lowercase first letter. If the name contains two or more words: Start with a capital letter each word after the first word (camel notation), e.g. myvariable Syntax type variablename; variablename = value; Example int counter; counter = 1; Declaration and initialization in one statement: int counter = 1; // declaration statement // assignment statement 1

2 3. Declaration and Initialization of Constants A constant is a name of memory location which stores a value that can t be changed Naming conventions: upper case first letter of each word in the name of the constant. (Pascal notation), e.g. InterestRate Syntax const type ConstantName = value; Examples const int DaysInNovember = 30; const decimal SalesTax =.075m; 4. Arithmetic Operations +, -, *, /, %, ++, -- Same as in Java and Python (except for / in Python) When both operands are integers, / gives the integer part of the division, e.g 5/3 = 1 % is the modulus operator: e.g. 5%3 = 2 ++ and -- have different action when in front or after the variable name. Example: a = 5; b = ++a; // after the operation we have a = 6, b = 6 a = 5; b = a++; // after the operation we have a = 6, b = 5 Arithmetic expressions that use characters char letter1 = 'C'; char letter2 = ++letter1; Precedence: ++, -- *, /, % +, - // letter1 = 'C' // Unicode integer is 67 // letter2 = 'D' // Unicode integer is 68 2

3 5. Assignment Syntax variablename = expression; Shortcuts: +=, -=, *=, /=, %= Used when the assignment statement involves same variable on the left and on the right. Example: x = x % 5 is the same as x %= 5 6. Type Casting Type casting changes the type of the data value a) Implicit - less precise to more precise byteshortintlongdecimal byteshortintdouble byteshortfloatdouble charint Works through assignment or operation Examples: double grade = 90; int code = A + 1; // converts int to double // converts char to int Note: No implicit cast between floating-point and decimal types. b) Explicit The target type is given in parentheses in front of the variable Example: double a = 12.8; int b = (int)(a * 4); // b is 51 int c = (int)a * 4; // c is 48 3

4 7. Static Methods of the Math Class Math.Round(decimalNumber[, precision, mode]) If one argument only round to a whole number Precision number of decimal digits If mode not specified a decimal value that ends in 5 is rounded to the nearest even decimal value mode = MidpointRounding.AwayFromZero will round positive values up and negative values down Examples: Math.Round(23.745, 2) Result: Math.Round(23.745, 2, MidpointRounding.AwayFromZero) Result: Math.Pow(number, power) Math.Sqrt(number) Math.{Min Max}(number1, number2) 8. Declaration and Initialization of Strings, String Operations A string: a sequence of characters enclosed in double quotes Null string: the value is not known Empty string: the string has 0 number of characters Examples: string message1 = "Invalid data entry."; string message2 = ""; // empty string string message3 = null; // null string, value unknown String concatenation: + string greeting = Hello + + firstname; Implicit type casting to strings: double price = 12.5; string pricestring = Price: $ + price; // pricestring is Price: $12.5 4

5 Escape sequences: \n New line \t Tab \r Return (the Enter key) \\ Backslash \ Quotes Verbatim string literals: in front of Example: string path c:\c#.net\files ; 9. Value Types and Reference Types Value types: The memory location associated with the variable contains the representation of the value assigned to that variable Reference types: The memory location associated with the variable contains a memory address where the object referred to by the variable is stored. Common.NET Structures that define value types Structure C# keyword What the value type holds Byte byte An 8-bit unsigned integer Int16 short A 16-bit signed integer Int32 int A 32-bit signed integer Int64 long A 64-bit signed integer Single float A single-precision floating-point number Double double A double-precision floating-point number Decimal decimal A 96-bit decimal value Boolean bool A true or false value Char char A single character.net classes that define reference types Class name C# keyword What the reference type holds String string A reference to a String object Object object A reference to any type of object 5

6 10. Methods for Data Conversion Value to string and string to value Method ToString([format]) Parse(string) Description A method that converts the value to its equivalent string representation using the specified format. If the format is omitted, the value isn t formatted. If the string can t be converted, an exception occurs A static method that converts the specified string to an equivalent data value. TryParse(string, result) A static method that converts the specified string to an equivalent data value and stores it in the result variable. Returns a true value if the string is converted. Otherwise, returns a false value. Static methods of the Convert class Method Description ToDecimal(value) Converts the value to the decimal data type. ToDouble(value) Converts the value to the double data type. ToInt32(value) Converts the value to the int data type. ToChar(value) Converts the value to the char data type. ToBool(value) Converts the value to the bool data type. ToString(value) Converts the value to a string object. Statements that use ToString, Parse, and TryParse decimal sales = m; string salesstring = sales.tostring(); sales = Decimal.Parse(salesString); Decimal.TryParse(salesString, out sales); // decimal to string // string to decimal // string to decimal Note: out in the second argument of TryParse is a keyword (see Ch6). If conversion can t be performed, 0 is stored in the variable ( sales in the example above) instead of throwing an exception. An implicit call of the ToString method double price = 49.50; string pricestring = "Price: $" + price; // automatic // ToString call 6

7 A TryParse method that handles invalid data string salesstring = "$ "; decimal sales = 0m; Decimal.TryParse(salesString, out sales); // sales is 0 Statements that use the Convert class // string to decimal decimal subtotal = Convert.ToDecimal(txtSubtotal.Text); // string to int int years = Convert.ToInt32(txtYears.Text); // decimal to string txtsubtotal.text = Convert.ToString(subtotal); // decimal to int int subtotalint = Convert.ToInt32(subtotal); 11. Convert Numbers to Formatted Strings Standard numeric formatting codes Code Format C or c Currency P or p Percent N or n Number F or f Float D or d Digits E or e Exponential G or g General How to use the ToString method to format a number Statement Example string monthlyamount = amount.tostring("c"); $1, string interestrate = interest.tostring("p1"); 2.3% string quantitystring = quantity.tostring("n0"); 15,000 string paymentstring = payment.tostring("f3");

8 How to use the Format method of the String class to format a number Statement Result string monthlyamount = String.Format("{0:c}", m); $1, string interestrate = String.Format("{0:p1}",.023m); 2.3% string quantitystring = String.Format("{0:n0}", 15000); 15,000 string paymentstring = String.Format("{0:f3}", ); The syntax of the format specification used by the Format method {index:formatcode} The index shows how many numbers will be formatted (0 if one number) 12. Scope of Variables Method variables: declared within a method, accessible within that method Class variables: declared in a class outside the class methods, accessible from all class methods 13. Enumerations An enumeration is a set of related constants that define a value type. Each constant is a member of that type enum EnumerationName [: type] { ConstantName1 [= value][, ConstantName2][= value]... } Example: enum TermValues : short { Net30Days = 30, Net60Days = 60, Net90Days = 90 } int k = (int)termvalues.net90days; // k is 90 string s = TermValues.Net90Days.toString(); // s is Net90Days 8

9 14. Nullable Types How to declare a value type that can contain null values int? quantity; quantity = null; quantity = 0; quantity = 20; decimal? salestotal = null; bool? isvalid = null; Terms? paymentterm = null; // string? message = null; // not necessary or allowed Two properties for working with nullable types Property HasValue Value Description Returns a true value if the nullable type contains a value. Returns a false value if the nullable type is null. Returns the value of the nullable type. How to check if a nullable type contains a value bool hasvalue = quantity.hasvalue; How to get the value of a nullable type int qty = quantity.value; How to use nullable types in arithmetic expressions decimal? sales1 = m; decimal? sales2 = null; decimal? salestotal = sales1 + sales2; // result = null 9

10 Learning Objectives After studying Chapter 4, you should be able to: 1. Given an arithmetic expression and the values for the variables in the expression, evaluate the expression. 2. Use numeric and string data as needed within your applications. That means you should be able to do any of the following: declare and initialize variables and constants code arithmetic expressions and assignment statements use the static methods of the Math class cast and convert data from one type to another use the correct scope for your variables declare and use enumerations 3. Distinguish between a variable and a constant and give the naming conventions for each. 4. Describe any of these data types: int, double, decimal, bool, and string. 5. Describe any of these terms: literal value, null value, empty string, concatenate, append, escape sequence, string literal, verbatim string literal, and nullable data type. 6. Describe the order of precedence for arithmetic expressions. 7. Distinguish between implicit casting and explicit casting. 8. Distinguish between a value type and a reference type. 9. Describe the differences in the ways that casting, the ToString method of a data structure, the Parse and TryParse methods of a data structure, and the methods of the Convert class can be used to convert data from one form to another. 10. Describe the differences between class scope and method scope. 10