Objectives. Data Types (continued) Data Types 4. การเข ยนโปรแกรมพ นฐาน ว ทยาการคอมพ วเตอร เบ องต น Fundamentals of Computer Science

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1 ว ทยาการคอมพ วเตอร เบ องต น Fundamentals of Computer Science ภาคการศ กษาท ภาคการศกษาท 1 ป ปการศกษา การศ กษา การเข ยนโปรแกรมพ นฐาน 4.2 ต วแปร น พจน และการก าหนดค า รวบรวมโดย อ. ดร. อาร ร ตน ตรงร ศม ทอง Objectives Data Types (ชน ดของต วแปร) Arithmetic Operations (การด าเน นการค านวณ) Variables and Declarations (ต วแปร และการก าหนดค า) Case Study: Temperature Conversion Common Programming and Compiler Errors A First Book of ANSI C, Fourth Edition 2 Data Types Data Types Data type: set of values and a set of operations that can be applied to these values Built in i dt data type: is provided d as an integral part of the language; also known as primitive type A First Book of ANSI C, Fourth Edition 3 A First Book of ANSI C, Fourth Edition 4 Data Types Data Types A literal is an acceptable value for a data type Also called a literal value or constant 2, 3.6, 8.2, and "Hello World!" are literal values because they literally display their values A First Book of ANSI C, Fourth Edition 5 A First Book of ANSI C, Fourth Edition 6 1

2 Integer Data Types Integer Data Types int: whole numbers (integers) For example: 0, -10, 253, Not allowed: commas, decimal points, special symbols char: stores individual characters (ASCII) For example: 'A', '$', 'b', '!' A First Book of ANSI C, Fourth Edition 7 A First Book of ANSI C, Fourth Edition 8 Integer Data Types Integer Data Types A First Book of ANSI C, Fourth Edition 9 A First Book of ANSI C, Fourth Edition 10 Integer Data Types Floating Point Data Types A floating point value (real number) can be the number zero or any positive or negative number that contains a decimal point For example: , 5., -6.2, , +2 Not allowed: commas, decimal points, special symbols float: single precision number double: double precision number Storage allocation for each data type depends on the compiler (use sizeof()) A First Book of ANSI C, Fourth Edition 11 A First Book of ANSI C, Fourth Edition 12 2

3 Floating Point Data Types Floating Point Data Types float literal is indicated by appending an f or F long double is created by appending an l or L indicates a double literal 9.234f indicates a float literal 9.234L indicates a long double literal A First Book of ANSI C, Fourth Edition 13 A First Book of ANSI C, Fourth Edition 14 Exponential Notation In numerical theory, the term precision typically refers to numerical accuracy Arithmetic Operations Arithmetic operators: operators used for arithmetic operations: Addition + Subtraction Multiplication li * Division / Modulus Division % Binary operators require two operands An operand can be either a literal value or an identifier that has a value associated with it A First Book of ANSI C, Fourth Edition 15 A First Book of ANSI C, Fourth Edition 16 Arithmetic Operations A simple binary arithmetic expression consists of a binary arithmetic operator connecting two literal values in the form: literalvalue operator literalvalue * / 2. Spaces around arithmetic operators are inserted for clarity and can be omitted without affecting the value of the expression Arguments are separated with commas printf("the total of 6 and 15 is %d", ); First argument of printf() must be a string A string that includes a conversion control sequence, such as %d, is termed a control string Conversion control sequences are also called conversion specifications and format specifiers printf() replaces a format specifier in its control string with the value of the next argument In this case, 21 A First Book of ANSI C, Fourth Edition 17 A First Book of ANSI C, Fourth Edition 18 3

4 printf("the total of 6 and 15 is %d", ); The total of 6 and 15 is 21 printf ("The sum of %f and %f is %f",, 12.2, , ); The sum of and is A First Book of ANSI C, Fourth Edition 19 A First Book of ANSI C, Fourth Edition 20 A First Book of ANSI C, Fourth Edition 21 A First Book of ANSI C, Fourth Edition 22 Expression Types Expression: any combination of operators and operands that can be evaluated to yield a value Integer expression: contains only integer operands; the result is an integer Floating point expression: contains only floatingpoint operands; the result is a double precision In a mixed mode expression the data type of each operation is determined by the following rules: If both operands are integers, result is an integer If one operand is real, result is double precision 15/2 = 7 Integer Division Integers cannot contain a fractional part Remainder is truncated % is the modulus or remainder operator 9 % 4 is 1 17 % 3 is 2 14 % 2 is 0 A First Book of ANSI C, Fourth Edition 23 A First Book of ANSI C, Fourth Edition 24 4

5 Negation Negation A unary operator is one that operates on a single operand, e.g., negation ( ) The minus sign in front of a single numerical value negates (reverses the sign of) the number A First Book of ANSI C, Fourth Edition 25 A First Book of ANSI C, Fourth Edition 26 Operator Precedence and Associativity Two binary arithmetic operator symbols must never be placed side by side Parentheses may be used to form groupings Expressions in parentheses are evaluated dfirst Parentheses may be enclosed by other parentheses Parentheses cannot be used to indicate multiplication Operator Precedence and Associativity Three levels of precedence: 1.All negations are done first 2.Multiplication, division, and modulus operations are computed next; expressions containing more than one of these operators are evaluated from left to right as each operator is encountered 3.Addition and subtraction are computed last; expressions containing more than one addition or subtraction are evaluated from left to right as each operator is encountered A First Book of ANSI C, Fourth Edition 27 A First Book of ANSI C, Fourth Edition 28 Operator Precedence and Associativity Operator Precedence and Associativity Example: * 7 % 2 * 4 = % 2 * 4 = * 4 = = 12 A First Book of ANSI C, Fourth Edition 29 A First Book of ANSI C, Fourth Edition 30 5

6 Variables and Declarations Variables and Declarations Variables are names given by programmers to computer storage Variable name usually limited to 255 characters Variable namesare are case sensitive A First Book of ANSI C, Fourth Edition 31 A First Book of ANSI C, Fourth Edition 32 Variables and Declarations Declaration Statements num1 = 45; num2 = 12; total = num1 + num2; Assignment statements Naming and specifying the data type that can be stored in each variable is accomplished using declaration statements Declaration statements within a function appear immediately after the opening brace of a function function name() { declaration statements; other statements; } Definition statements define or tell the compiler how much memory is needed for data storage A First Book of ANSI C, Fourth Edition 33 A First Book of ANSI C, Fourth Edition 34 Declaration Statements Declaration Statements A First Book of ANSI C, Fourth Edition 35 A First Book of ANSI C, Fourth Edition 36 6

7 Declaration Statements Declaration Statements A First Book of ANSI C, Fourth Edition 37 A First Book of ANSI C, Fourth Edition 38 Declaration Statements Selecting Variable Names You can omit the f and let the compiler convert the double precision value into a float value when the assignment is made Make variable names descriptive Limit variable names to approximately 20 characters Start the variable ibl name with iha letter, rather than an underscore (_) In a variable name consisting of several words, capitalize the first letter of each word after the first A First Book of ANSI C, Fourth Edition 39 A First Book of ANSI C, Fourth Edition 40 Selecting Variable Names Use variable names that indicate what the variable corresponds to, rather than how it is computed Add qualifiers, such as Avg, Min, Max, and Sum to complete a variable s name where appropriate Use single letter variable names, such as i, j, and k, for loop indexes Initialization Declaration statements can be used to store an initial value into declared variables int numone = 15; When a declaration statement provides an initial value, the variable is said to be initialized Literals, expressions using only literals such as , and expressions using literals and previously initialized variables can all be used as initializers within a declaration statement A First Book of ANSI C, Fourth Edition 41 A First Book of ANSI C, Fourth Edition 42 7

8 Case Study: Temperature Conversion A friend of yours is going to Spain, where temperatures are reported using the Celsius temperature scale. She has asked you to provide her with a list of temperatures in degrees Fahrenheit, and the equivalent temperaturein degrees Celsius. The formula relating the two temperatures is Celsius = 5/9(Fahrenheit 32). Initially, you are to write and test a program that correctly converts the Fahrenheit temperature of 75 degrees into its Celsius equivalent. Case Study: Temperature Conversion A First Book of ANSI C, Fourth Edition 43 A First Book of ANSI C, Fourth Edition 44 Common Programming Errors Forgetting to declare all the variables used in a program Storing an incorrect data type in a declared variable Using a variable in an expression before a value has been assigned to the variable Dividing integer values incorrectly Mixing data types in the same expression without clearly understanding the effect produced A First Book of ANSI C, Fourth Edition 45 Common Programming Errors Not including the correct conversion control sequence in printf() function calls for the data types of the remaining arguments Not closing the control string in printf() with a double quote symbol followed by a comma when additional arguments are passed to printf() Forgetting to separate all arguments passed to printf() with commas A First Book of ANSI C, Fourth Edition 46 Common Compiler Errors Common Compiler Errors A First Book of ANSI C, Fourth Edition 47 A First Book of ANSI C, Fourth Edition 48 8

9 Summary The printf() function displays text or numerical results The two basic numerical data types used almost exclusively in current C programs are integers and double precision numbers An expression is a sequence of one or more operands separated by operators Expressions are evaluated according to the precedence and associativity of the operators A First Book of ANSI C, Fourth Edition 49 used Summary printf() can display all of C s data types Every variable in a C program must be Declared with a data type Used after it is declared Declaration statements inform the compiler of a function s valid variable names A First Book of ANSI C, Fourth Edition 50 9