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Chapter 2 C++ Syntax and Semantics, and the Program Development Process

Programming in C++. Chapter 2 C++ Syntax and Semantics, and the Program Development Process. End of Line Manipulator. Two ways of doing this cout &lt;&lt;“The State of Pennsylvania<br>” &lt;&lt; “is where Penn State University is located.<br>”;

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Chapter 2 C++ Syntax and Semantics, and the Program Development Process

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  1. Programming in C++ Chapter 2 C++ Syntax and Semantics, and the Program Development Process

  2. End of Line Manipulator • Two ways of doing this • cout <<“The State of Pennsylvania\n” << “is where Penn State University is located.\n”; • cout <<“The State of Pennsylvania” << endl <<“is where Penn State University is located.” << endl; • Good programming is to always end your program with a \n or endl

  3. Identifiers • Identifiers (i.e. variables) are the very core of programming languages • Programs are constructed so as to manipulate numbers, letter, and characters • Identifiers (variables) hold numbers usually

  4. Identifiers • The strength of a identifier is that its value is easily changed • Identifiers are case sensitive • forest is different from forEst • Good programming uses identifiers that relate to the data and the program • Goof programming uses a consistent method of creating identifiers

  5. Identifiers • An identifier must start with a letter or underscore, and be followed by zero or more letters (A-Z, a-z), digits (0-9), or underscores. • VALID age_of_dog TaxRate98 PrintHeading AgeOfHorse • NOT VALID (Why?) age# 98TaxRate Age-Of-Cat

  6. More about Identifiers • Some C++ compilers recognize only the first 32 characters of an identifier as significant. • Then these identifiers are considered the same: Age_Of_This_Old_Rhinoceros_At_My_Zoo Age_Of_This_Old_Rhinoceros_At_My_Safari • What about these? Age_Of_This_Old_Rhinoceros_At_My_Zoo AgE_Of_This_Old_Rhinoceros_At_My_Zoo

  7. More about Identifiers • C++ has certain reserved words that have a predetermined meaning and are not be be used as identifiers • e.g. int, long, float, return, short • see Appendix A of text for a list of these reserved words • “do not” use reserved words as identifiers, else there will be a programming problem

  8. Identifiers • Every identifier (variable) in a C++ program must be declared before it is used • before being used • at the start of the “main” part of the program • Separate declarations of variables by a comma when they are in the same statement

  9. Address pointer reference C++ Data Types Simple Structured Integral Floating array struct union class char short int long enum float double long double

  10. C++ Simple Data Types Simple types Floating Integral char short int long enum float double long double unsigned

  11. Fundamental Data Types in C++ • Integral Types • represent whole numbers and their negatives • declared as int, short, orlong • Floating Types • represent real numbers with a decimal point • declared as float, or double • Character Type • can be letters, single digits, symbols, punctuation • declared as char

  12. Samples of C++ Data Values int sample values 4578 -4578 0 doublesample values 95.274 95. .265 9521E-3 -95E-1 95.213E2 char sample values ‘B’‘d’ ‘4’‘?’‘*’

  13. Scientific Notation 2.7E4 means 2.7 x 10 4 = 2.7000 = 27000.0 2.7E-4 means 2.7 x 10 - 4 = 0002.7 = 0.00027

  14. Size of Varibles • Program to calculate size of allowed variables • short int 2 bytes -32,768 to 32,767 • long int 4 bytes -2,147,483,648 to 2,147,483,648 • float 4 bytes 1.2e-38 to 3.4e38 • double 8 bytes 2.2e-308 to 1.8e308

  15. Program Variable Sizes • //Finding the size of varible types used by your computer • #include <iostream.h> • int main() • { • cout << "The size of an int is:\t\t" << sizeof(int) • << " bytes.\n"; • cout << "The size of a short int is:\t\t" << sizeof(short) • << " bytes.\n"; • cout << "The size of a long int is:\t\t" << sizeof(long) • << " bytes.\n"; • cout << "The size of a char is:\t\t" << sizeof(char) • << " bytes.\n"; • cout << "The size of a float is:\t\t" << sizeof(float) • << " bytes.\n"; • cout << "The size of a double is:\t\t" << sizeof(double) • << " bytes.\n"; • return 0;

  16. More About Floating Point Values • Floating point numbers have an integer part and a fractional part, with a decimal point in between. Either the integer part or the fractional part, but not both, may be missing. EXAMPLES 18.4 500. .8 -127.358 • Alternatively, floating point values can have an exponent, as in scientific notation. The number preceding the letter E doesn’t need to include a decimal point. EXAMPLES 1.84E1 5E2 8E-1 -.127358E3

  17. Understanding Types • Is 5,123 a valid integer constant? • No, commas are not allowed • Is 5.8e24 a valid floating point constant? • Yes • Is 0.0 a valid floating point constant? • Yes • Is “Float” a reserved word? • No, but “float” is

  18. What is a Variable? • A variableis a location in memorywhich we can refer to by an identifier, and in which a data value that can be changed is stored.

  19. What Does a Variable Declaration Do? int Age_Of_Dog; float TaxRate98; char MiddleInitial; A declaration tells the compiler to allocate enough memoryto hold a value of this data type, and to associate the identifierwith this location. 4 bytes for TaxRate98 1 byte for MiddleInitial

  20. Giving a value to a variable In your program you can assign (give) a value to the variable by using the assignment operator = Age_Of_Dog = 12; or by another method, such as cout << “How old is your dog?”; cin >> Age_Of_Dog;

  21. What is a Named Constant? • A named constantis a location in memorywhich we can refer to by an identifier, and in which a data value that cannot be changed is stored. VALID CONSTANT DECLARATIONS const char STAR = ‘*’ ; const float NORMAL_TEMP = 98.6 ; const float PI = 3.14159 ; const float TAX_RATE = 0.0725 ; const int MAX_SIZE = 50 ; const int VOTING_AGE = 18 ;

  22. says no parameters type of returned value name of function Simplest C++ Program int main (void) { return 0; }

  23. A Block (or Compound Statement) • A block is a sequence of zero or more statements enclosed by a pair of curly braces { }. SYNTAX { Statement(optional) . . . }

  24. main Returns an Integer to the Operating System //*************************************************************************** // FreezeBoil program // This program computes the midpoint between // the freezing and boiling points of water //*************************************************************************** #include < iostream.h> const float FREEZE_PT = 32.0 ; // Freezing point of water const float BOIL_PT = 212.0 ; // Boiling point of water int main ( void ) { float avgTemp ; // Holds the result of averaging // FREEZE_PT and BOIL_PT

  25. Function main Continued cout << “Water freezes at “ << FREEZE_PT << endl ; cout << “ and boils at “ << BOIL_PT << “ degrees.” << endl ; avgTemp = FREEZE_PT + BOIL_PT ; avgTemp = avgTemp / 2.0 ; cout << “Halfway between is “ ; cout << avgTemp << “ degrees.” << endl ; return 0 ; }

  26. Is compilation the first step? • No. Before your source program is compiled, it is first examined by the preprocessorto • Remove all comments from source code • Handle all preprocessor directives. They begin with the # character such as #include <iostream.h> • Tells preprocessor to look in the standard include directory for the header file called iostream.h and insert its contents into your source code.

  27. Using Libraries • A library has 2 parts Interface (stored in a header file) tells what items are in the library and how to use them. Implementation (stored in another file) contains the definitions of the items in the library. • #include <iostream.h> Refers to the header file for the iostream library needed for use of cin and cout.

  28. Mileage Program /* This program computes miles per gallon given four amounts for gallons used, and starting and ending mileage. Constants: The gallon amounts for four fillups. The starting mileage. The ending mileage. Output (screen) The calculated miles per gallon. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -*/ #include <iostream.h>

  29. C++ Code Continued const float AMT1 = 11.7 ; // Number of gallons for fillup 1 const float AMT2 = 14.3 ; // Number of gallons for fillup 2 const float AMT3 = 12.2 ; // Number of gallons for fillup 3 const float AMT4 = 8.5 ; // Number of gallons for fillup 4 const float START_MILES = 67308.0 ; // Starting mileage const float END_MILES = 68750.5 ; // Ending mileage int main(void) { float mpg ; // Computed miles per gallon mpg = (END_MILES - START_MILES) / (AMT1 + AMT2 + AMT3 + AMT4) ;

  30. main Returns an Integer Value to the Operating System cout << “For the gallon amounts “ << endl ; cout << AMT1 << ‘ ‘ << AMT2 << ‘ ‘ << AMT3 << ‘ ‘ << AMT4 << endl ; cout << “and a starting mileage of “ << START_MILES << endl ; cout << “and an ending mileage of “ << END_MILES << endl ; cout << “the mileage per gallon is “ << mpg << endl ; return 0; }

  31. What is an Expression in C++? • An expression is any valid combination of operators and operands. • In C++ each expression has a value. • The value of the expression 9.3 * 4.5 is 41.85

  32. Division Operator • The result of the division operator depends on the type of its operands. • If one or both operands has a floating point type, the result is a floating point type. Otherwise, the result is an integer type. • Examples 11 / 4 has value 2 11.0 / 4.0 has value 2.75 11 / 4.0 has value 2.75

  33. Modulus Operator • The modulus operator % can only be used with integer type operands and always has an integer type result. • Its result is the integer typeremainderof an integer division. • EXAMPLE 11 % 4 has value 3 because R = ? ) 4 11

  34. More C++ Operators int Age; Age = 8; Age = Age + 1; 8 Age 9 Age

  35. PREFIX FORMIncrement Operator int Age; Age = 8; ++Age; 8 Age 9 Age

  36. POSTFIX FORM Increment Operator int Age; Age = 8; Age++; 8 Age 9 Age

  37. Decrement Operator int Dogs; Dogs = 100; Dogs--; 100 Dogs 99 Dogs

  38. Which form to use?? • When the increment (or decrement) operator is used in a “stand alone” statementsolely to add one (or subtract one) from a variable’s value, it can be used in either prefix or postfix form. USE EITHER Dogs--;--Dogs ;

  39. BUT... • When the increment (or decrement) operator is used in a statement with other operators, the prefix and postfix forms can yield different results. WE’LL SEE HOW LATER . . .

  40. Insertion Operator ( << ) • Variablecoutis predefined to denote an output stream that goes to the standard output device (display screen). • The insertion operator << called “put to” takes 2 operands. • The left operand is a stream expression, such as cout. The right operand is an expression of simple type or a string constant.

  41. Output Statements SYNTAX These examples yield the same output. cout << “The answer is “ ; cout << 3 * 4 ; cout << “The answer is “ << 3 * 4 ; cout << ExprOrString << ExprOrString . . . ;

  42. Function definition Parameter of function Name of function Function Concept in Math f ( x ) = 5 x - 3 When x = 1, f ( x ) = 2 is the returned value. When x = 4, f ( x ) = 17 is the returned value. Returned value is determined by the function definition and by the values of any parameters.

  43. A C++ program is a collection of one or more functions • There must be a function called main( ) • Execution begins with the first statement in function main( ) • Any other functions in your program are subprograms and are not executed until they are called.

  44. Program with several functions main( ) function Square( ) function Cube( ) function

  45. Program with Three Functions #include <iostream.h> int Square ( int ) ; // declares these 2 functions int Cube ( int ) ; int main ( void ) { cout << “The square of 27 is “ << Square (27) << endl ; // function call cout << “The cube of 27 is “ << Cube (27) << endl ; // function call return 0 ; }

  46. Rest of Program int Square ( int n ) { return n * n ; } int Cube ( int n ) { return n * n * n ; }

  47. Output of program The square of 27 is 729 The cube of 27 is 19683

  48. Before Next Class • Go to a computer lab and type in and run mileage program on page 49 of text • Try programming and running program exercise 3 on page 58 of text

  49. What Next Class Will Cover • Any questions from last class session • Complete chapter 2 • Class discussion of review questions for better understanding of chapter 2 • Programming examples provided • Recommended Chapter 2 practice questions

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