01 c++ Intro.ppt

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01 c++ Intro.ppt

  1. 1. C++
  2. 2. The Task of Programming <ul><li>Programming a computer involves writing instructions that enable a computer to carry out a single task or a group of tasks </li></ul><ul><li>A computer programming language requires learning both vocabulary and syntax </li></ul><ul><li>Programmers use many different programming languages, including BASIC, Pascal, COBOL, RPG, and C++ </li></ul><ul><li>The rules of any language make up its syntax </li></ul><ul><li>Machine language is the language that computers can understand; it consists of 1s and 0s </li></ul>1
  3. 3. The Task of Programming <ul><li>A translator (called either a compiler or an interpreter) checks your program for syntax errors </li></ul><ul><li>A logical error occurs when you use a statement that, although syntactically correct, doesn’t do what you intended </li></ul><ul><li>You run a program by issuing a command to execute the program statements </li></ul><ul><li>You test a program by using sample data to determine whether the program results are correct </li></ul>1
  4. 4. Programming Universals <ul><li>All programming languages provide methods for directing output to a desired object, such as a monitor screen, printer or file </li></ul><ul><li>Similarly, all programming languages provide methods for sending input into the computer program so that it can be manipulated </li></ul><ul><li>In addition, all programming languages provide for naming locations in computer memory </li></ul><ul><li>These locations commonly are called variables (or attributes ) </li></ul>1
  5. 5. Programming Universals <ul><li>Ideally, variables have meaningful names, although no programming language actually requires that they meet this standard </li></ul><ul><li>A variable may have only one value at a time, but it is the ability of memory variables to change in value that makes computers and programming worthwhile </li></ul><ul><li>In many computer programming languages, including C++, variables must be explicitly declared , or given a data type as well as a name, before they can be used </li></ul>1
  6. 6. Programming Universals <ul><li>The type determines what kind of values may be stored in a variable </li></ul><ul><li>Most computer languages allow at least two types: one for numbers and one for characters </li></ul><ul><li>Numeric variables hold values like 13 or -6 </li></ul><ul><li>Character variables hold values like ‘A’ or ‘&’ </li></ul><ul><li>Many languages include even more specialized types, such as integer (for storing whole numbers) or floating point (for storing numbers with decimal places) </li></ul>1
  7. 7. Procedural Programming <ul><li>Procedural programs consist of a series of steps or procedures that take place one after the other </li></ul><ul><li>The programmer determines the exact conditions under which a procedure takes place, how often it takes place, and when the program stops </li></ul><ul><li>Programmers write procedural programs in many programming languages, such as COBOL, BASIC, FORTRAN, and RPG </li></ul><ul><li>You can also write procedural programs in C++ </li></ul>1
  8. 8. A main( ) Function in C++ <ul><li>C++ programs consist of modules called functions </li></ul><ul><li>Every statement within every C++ program is contained in a function </li></ul><ul><li>Every function consists of two parts: </li></ul><ul><ul><li>A function header is the initial line of code in a C++ which always has three parts: </li></ul></ul><ul><ul><ul><li>Return type of the function </li></ul></ul></ul><ul><ul><ul><li>Name of the function </li></ul></ul></ul><ul><ul><ul><li>Types and names of any variables enclosed in parentheses, and which the function receives </li></ul></ul></ul><ul><ul><li>A function body </li></ul></ul>1
  9. 9. Creating a main( ) Function <ul><li>A C++ program may contain many functions, but every C++ program contains at least one function, and that function is called main( ) </li></ul><ul><li>If the main function does not pass values to other programs or receives values from outside the program, then main( ) receives and returns a void type </li></ul><ul><li>The body of every function in a C++ program is contained in curly braces, also known as curly brackets </li></ul>1
  10. 10. Creating a main( ) Function <ul><li>Every complete C++ statement ends with a semicolon </li></ul><ul><li>Often several statements must be grouped together, as when several statements must occur in a loop </li></ul><ul><li>In such a case, the statements have their own set of opening and closing braces within the main braces, forming a block </li></ul>1
  11. 11. Working with Variables <ul><li>In C++, you must name and give a type to variables (sometimes called identifiers ) before you can use them </li></ul><ul><li>Names of C++ variables can include letters, numbers, and underscores, but must begin with a letter or underscore </li></ul><ul><li>No spaces or other special characters are allowed within a C++ variable name </li></ul><ul><li>Every programming language contains a few vocabulary words, or keywords , that you need in order to use the language </li></ul>1
  12. 12. Common C++ Keywords
  13. 13. Working with Variables <ul><li>A C++ keyword cannot be used as a variable name </li></ul><ul><li>Each named variable must have a type </li></ul><ul><li>C++ supports three simple types: </li></ul><ul><ul><li>Integer — Floating point — Character </li></ul></ul><ul><li>An integer is a whole number, either positive or negative </li></ul><ul><li>An integer value may be stored in an integer variable declared with the keyword int </li></ul><ul><li>You can also declare an integer variable using short int and long int </li></ul>1
  14. 14. Working with Variables <ul><li>Real or floating-point numbers are numbers that include decimal positions, such as 98.6, 1000.00002, and -3.85 </li></ul><ul><li>They may be stored in variables with type float, double , and long double </li></ul><ul><li>Characters may be stored in variables declared with the keyword char </li></ul><ul><li>A character may hold any single symbol in the ASCII character set </li></ul><ul><li>Often it contains a letter of the alphabet, but it could include a space, digit, punctuation mark, arithmetic symbol, or other special symbol </li></ul>1
  15. 15. Working with Variables <ul><li>In C++, a character value is always expressed in single quotes, such as ‘A’ or ‘&’ </li></ul><ul><li>To declare a variable, you list its type and its name </li></ul><ul><li>In addition, a variable declaration is a C++ statement, so it must end with a semicolon </li></ul><ul><li>If you write a function that contains variables of diverse types, each variable must be declared in a statement of its own </li></ul><ul><li>If you want to declare two or more variables of the same type, you may declare them in the same statement </li></ul>
  16. 16. Working with Variables <ul><li>Explicitly stating the value of a variable is called assignment , and is achieved with the assignment operator = </li></ul><ul><li>The variable finalScore is declared and assigned a value at the same time </li></ul><ul><li>Assigning a value to a variable upon creation is often referred to as initializing the variable </li></ul>1
  17. 17. The const Qualifier <ul><li>A variable that does not change in a program should not be declared as a variable </li></ul><ul><li>Instead, it should be a constant </li></ul><ul><li>The statement const double MINIMUM_WAGE = 5.75; declares a constant named MINIMUM_WAGE that can be used like a variable, but cannot be changed during a program </li></ul>1
  18. 18. Creating Comments <ul><li>Comments are statements that do not affect the compiling or running of a program </li></ul><ul><li>Comments are simply explanatory remarks that the programmer includes in a program to clarify what is taking place </li></ul><ul><li>These remarks are useful to later program users because they might help explain the intent of a particular statement or the purpose of the entire program </li></ul><ul><li>C++ supports both line comments and block comments </li></ul>1
  19. 19. Creating Comments <ul><li>A line comment begins with two slashes (//) and continues to the end of the line on which it is placed </li></ul><ul><li>A block comment begins with a single slash and an asterisk (/*) and ends with an asterisk and a slash (*/); it might be contained on a single line or continued across many lines </li></ul>1
  20. 20. Using Libraries and Preprocessor Directives <ul><li>Header files are files that contain predefined values and routines, such as sqrt( ) </li></ul><ul><li>Their filenames usually end in .h </li></ul><ul><li>In order for your C++ program to use these predefined routines, you must include a preprocessor directive , a statement that tells the compiler what to do before compiling the program </li></ul><ul><li>In C++, all preprocessor directives begin with a pound sign (#), which is also called an octothorp </li></ul><ul><li>The #include preprocessor directive tells the compiler to include a file as part of the finished product </li></ul>1
  21. 21. C++ Binary Arithmetic Operators <ul><li>Often after data values are input, you perform calculations with them </li></ul><ul><li>C++ provides five simple arithmetic operators for creating arithmetic expressions: </li></ul><ul><ul><li>addition (+) – subtraction (-) </li></ul></ul><ul><ul><li>multiplication (*) – division (/) </li></ul></ul><ul><ul><li>modulus (%) </li></ul></ul><ul><li>Each of these arithmetic operators is a binary operator; each takes two operands, one on each side of the operator, as in 12 + 9 or 16.2*1.5 </li></ul><ul><li>The results of an arithmetic operation can be stored in memory </li></ul>2
  22. 22. C++ Binary Arithmetic Operators 2
  23. 23. C++ Binary Arithmetic Operators <ul><li>In Figure 2-2, each operation is assigned to a result variable of the correct type </li></ul><ul><li>The expression a + b has an integer result because both a and b are integers, not because their sum is stored in the intResult variable </li></ul><ul><li>If the program contained the statement doubleResult = a+b; the expression a+b would still have an integer value, but the value would be cast , or transformed, into a double when the sum is assigned to doubleResult </li></ul>2
  24. 24. C++ Binary Arithmetic Operators <ul><li>The automatic cast that occurs when you assign a value of one type to another is called an implicit cast </li></ul><ul><li>The modulus operator (%), which gives the remainder of integer division, can be used only with integers </li></ul><ul><li>When more than one arithmetic operator is included in an expression, then multiplication, division, and modulus operations always occur before addition or subtraction </li></ul><ul><li>Multiplication, division, and modulus are said to have higher precedence </li></ul>2
  25. 25. Shortcut Arithmetic Operators <ul><li>C++ employs several shortcut operators </li></ul><ul><li>When you add two variable values and store the result in a third variable, the expression takes the form result= firstValue + secondValue </li></ul><ul><li>When you use an expression like this, both firstValue and secondValue retain their original values; only the result is altered </li></ul><ul><li>When you want to increase a value, the expression takes the form firstValue = firstValue + secondValue </li></ul>2
  26. 26. Shortcut Arithmetic Operators <ul><li>C++ provides the -= operator for subtracting one value from another, the *= operator for multiplying one value by another, and the /= operator for dividing one value by another </li></ul><ul><li>As with the += operator, you must not insert a space within the subtraction, multiplication, or division shortcut operators </li></ul><ul><li>The options shown in Figure 2-4 means replace the current value of count with the value that is 1 more than count, or simply increment count </li></ul>2
  27. 27. Shortcut Arithmetic Operators <ul><li>As you might expect, you can use two minus signs (--) before or after a variable to decrement it </li></ul>2
  28. 28. Shortcut Arithmetic Operators <ul><li>The prefix and postfix increment and decrement operators are examples of unary operators </li></ul><ul><li>Unary operators are those that require only one operand, such as num in the expression ++num </li></ul><ul><li>When an expression includes a prefix operator, the mathematical operation takes place before the expression is evaluated </li></ul><ul><li>When an expression includes a postfix operator, the mathematical operation takes place after the expression is evaluated </li></ul>2
  29. 29. Shortcut Arithmetic Operators <ul><li>The difference between the results produced by the prefix and postfix operators can be subtle, but the outcome of a program can vary greatly depending on which increment operator you use in an expression </li></ul>2
  30. 30. Evaluating Boolean Expressions <ul><li>A boolean expression is one that evaluates as true or false </li></ul><ul><li>All false relational expressions are evaluated as 0 </li></ul><ul><li>Thus, an expression such as 2>9 has the value 0 </li></ul><ul><li>You can prove that 2>9 is evaluated as 0 by entering the statement code <<(2>9); into a C++ program </li></ul><ul><li>A 0 appears on output </li></ul><ul><li>All true relational expressions are evaluated as 1 </li></ul><ul><li>Thus, the expression 9>2 has the value 1 </li></ul>2
  31. 31. Evaluating Boolean Expressions <ul><li>The unary operator ! Means not, and essentially reverses the true/false value of an expression </li></ul>2
  32. 32. Selection <ul><li>Computer programs seem smart because of their ability to use selections or make decisions </li></ul><ul><li>C++ lets you perform selections in a number of ways: </li></ul><ul><ul><li>The if statement </li></ul></ul><ul><ul><li>The switch statement </li></ul></ul><ul><ul><li>The if operator </li></ul></ul><ul><ul><li>Logical AND and Logical OR </li></ul></ul>2
  33. 33. Some Sample Selection Statements within a C++ Program 2
  34. 34. The if Statement <ul><li>If the execution of more than one statement depends on the selection, then the statements must be blocked with curly braces as shown in the code segment in Figure 2-8 </li></ul>2
  35. 35. The if Statement 2
  36. 36. Multiple Executable Statement in an if-else 2
  37. 37. The if Statement <ul><li>Any C++ expression can be evaluated as part of an if statement </li></ul>2
  38. 38. The switch Statement <ul><li>When you want to create different outcomes depending on specific values of a variable, you can use a series of ifs shown in the program statement in Figure 2-14 </li></ul><ul><li>As an alternative to the long string of ifs shown in Figure 2-14, you can use the switch statement </li></ul><ul><li>The switch can contain any number of cases in any order </li></ul>2
  39. 39. The if Operator <ul><li>Another alternative to the if statement involves the if operator (also called the conditional operator ), which is represented by a question mark (?) </li></ul><ul><li>E.g. </li></ul><ul><li>cout<<(driveAge<26)?”The driver is under 26”:”The driver is at least 26”; </li></ul><ul><li>The if operator provides a concise way to express two alternatives </li></ul><ul><li>The conditional operator is an example of a ternary operator, one that takes three operands instead of just one or two </li></ul>2
  40. 40. Logical AND and Logical OR <ul><li>In some programming situations, two or more conditions must be true to initiate an action </li></ul><ul><li>Figure 2-16 works correctly using a nested if —that is, one if statement within another if statement </li></ul><ul><li>If numVisits is not greater than 5, the statement is finished—the second comparison does not even take place </li></ul><ul><li>Alternatively, a logical AND (&&) can be used, as shown in Figure 2-17 </li></ul>2
  41. 41. Logical AND and Logical OR 2
  42. 42. Logical AND and Logical OR <ul><li>A logical AND is a compound boolean expression in which two conditions must be true for the entire expression to evaluate as true </li></ul><ul><li>Table 2-3 shows how an expression using && is evaluated </li></ul><ul><li>An entire expression is true only when the expression on each side of the && is true </li></ul>2
  43. 43. Using the Logical OR <ul><li>In certain programming situations, only one of two alternatives must be true for some action to take place </li></ul><ul><li>A logical OR (||) could also be used </li></ul><ul><li>A logical OR is a compound boolean expression in which either of two conditions must be true for the entire expression to evaluate as true </li></ul><ul><li>Table 2-4 shows how C++ evaluates any expression that uses the || operator </li></ul>2
  44. 44. Using the Logical OR 2
  45. 45. Using the Logical OR <ul><li>When either expression1 or expression2 is true (or both are true), the entire expression is true </li></ul><ul><li>On pages 53 and 54 of the textbook, perform the steps so you can write a program that makes several decisions </li></ul>2
  46. 46. A Typical Run of the Decisions.cpp Program 2
  47. 47. The while Loop <ul><li>Loops provide a mechanism with which to perform statements repeatedly and, just as important, to stop that performance when warranted </li></ul><ul><ul><li>while (boolean expression) </li></ul></ul><ul><ul><li>statement; </li></ul></ul><ul><li>In C++, the while statement can be used to loop </li></ul><ul><li>The variable count, shown in the program in Figure 2-21, is often called a loop-control variable , because it is the value of count that controls whether the loop body continues to execute </li></ul>2
  48. 48. The while Loop 2
  49. 49. The while Loop 2
  50. 50. The for Statement <ul><li>The for statement represents an alternative to the while statement </li></ul><ul><li>It is most often used in a definite loop , or a loop that must execute a definite number of times </li></ul><ul><li>It takes the form: </li></ul><ul><ul><li>for ( initialize; evaluate; alter) </li></ul></ul><ul><ul><li>statement ; </li></ul></ul>2

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