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C++ basic.ppt
- 1. Learning Objectives • Introduction to C++ – Origins, Object-Oriented Programming, Terms • Variables, Expressions, and Assignment Statements • Console Input/Output • Program Style • Libraries and Namespaces
- 2. Introduction to C++ • C++ Origins – Low-level languages • Machine, assembly – High-level languages • C, C++, ADA, COBOL, FORTRAN – Object-Oriented-Programming in C++ • C++ Terminology – Programs and functions – Basic Input/Output (I/O) with cin and cout
- 3. Display 1.1 A Sample C++ Program (1 of 2)
- 4. C++ Variables • C++ Identifiers – Keywords/reserved words vs. Identifiers – Case-sensitivity and validity of identifiers – Meaningful names! • Variables – A memory location to store data for a program – Must declare all data before use in program
- 5. Data Types: Display 1.2 Simple Types (1 of 2)
- 6. Data Types: Display 1.2 Simple Types (2 of 2)
- 7. Assigning Data • Initializing data in declaration statement – Results "undefined" if you don’t! • int myValue = 0; • Assigning data during execution – Lvalues (left-side) & Rvalues (right-side) • Lvalues must be variables • Rvalues can be any expression • Example: distance = rate * time; Lvalue: "distance" Rvalue: "rate * time"
- 8. Assigning Data: Shorthand Notations • Display, page 14
- 9. Data Assignment Rules • Compatibility of Data Assignments – Type mismatches • General Rule: Cannot place value of one type into variable of another type – intVar = 2.99; // 2 is assigned to intVar! • Only integer part "fits", so that’s all that goes • Called "implicit" or "automatic type conversion" – Literals • 2, 5.75, "Z", "Hello World" • Considered "constants": can’t change in program
- 10. Literal Data • Literals – Examples: • 2 // Literal constant int • 5.75 // Literal constant double • "Z" // Literal constant char • "Hello World" // Literal constant string • Cannot change values during execution • Called "literals" because you "literally typed" them in your program!
- 11. Escape Sequences • "Extend" character set • Backslash, preceding a character – Instructs compiler: a special "escape character" is coming – Following character treated as "escape sequence char" – Display 1.3 next slide
- 12. Display 1.3 Some Escape Sequences (1 of 2)
- 13. Display 1.3 Some Escape Sequences (2 of 2)
- 14. Constants • Naming your constants – Literal constants are "OK", but provide little meaning • e.g., seeing 24 in a pgm, tells nothing about what it represents • Use named constants instead – Meaningful name to represent data const int NUMBER_OF_STUDENTS = 24; • Called a "declared constant" or "named constant" • Now use it’s name wherever needed in program • Added benefit: changes to value result in one fix
- 15. Arithmetic Operators: Display 1.4 Named Constant (1 of 2) • Standard Arithmetic Operators – Precedence rules – standard rules
- 16. Arithmetic Operators: Display 1.4 Named Constant (2 of 2)
- 17. Arithmetic Precision • Precision of Calculations – VERY important consideration! • Expressions in C++ might not evaluate as you’d "expect"! – "Highest-order operand" determines type of arithmetic "precision" performed – Common pitfall!
- 18. Arithmetic Precision Examples • Examples: – 17 / 5 evaluates to 3 in C++! • Both operands are integers • Integer division is performed! – 17.0 / 5 equals 3.4 in C++! • Highest-order operand is "double type" • Double "precision" division is performed! – int intVar1 =1, intVar2=2; intVar1 / intVar2; • Performs integer division! • Result: 0!
- 19. Individual Arithmetic Precision • Calculations done "one-by-one" – 1 / 2 / 3.0 / 4 performs 3 separate divisions. • Firstïƒ 1 / 2 equals 0 • Thenïƒ 0 / 3.0 equals 0.0 • Thenïƒ 0.0 / 4 equals 0.0! • So not necessarily sufficient to change just "one operand" in a large expression – Must keep in mind all individual calculations that will be performed during evaluation!
- 20. Type Casting • Casting for Variables – Can add ".0" to literals to force precision arithmetic, but what about variables? • We can’t use "myInt.0"! – static_cast<double>intVar – Explicitly "casts" or "converts" intVar to double type • Result of conversion is then used • Example expression: doubleVar = static_cast<double>intVar1 / intVar2; – Casting forces double-precision division to take place among two integer variables!
- 21. Type Casting • Two types – Implicit—also called "Automatic" • Done FOR you, automatically 17 / 5.5 This expression causes an "implicit type cast" to take place, casting the 17 ïƒ 17.0 – Explicit type conversion • Programmer specifies conversion with cast operator (double)17 / 5.5 Same expression as above, using explicit cast (double)myInt / myDouble More typical use; cast operator on variable
- 22. Shorthand Operators • Increment & Decrement Operators – Just short-hand notation – Increment operator, ++ intVar++; is equivalent to intVar = intVar + 1; – Decrement operator, -- intVar--; is equivalent to intVar = intVar – 1;
- 23. Shorthand Operators: Two Options • Post-Increment intVar++ – Uses current value of variable, THEN increments it • Pre-Increment ++intVar – Increments variable first, THEN uses new value • "Use" is defined as whatever "context" variable is currently in • No difference if "alone" in statement: intVar++; and ++intVar; ïƒ identical result
- 24. Post-Increment in Action • Post-Increment in Expressions: int n = 2, valueProduced; valueProduced = 2 * (n++); cout << valueProduced << endl; cout << n << endl; – This code segment produces the output: 4 3 – Since post-increment was used
- 25. Pre-Increment in Action • Now using Pre-increment: int n = 2, valueProduced; valueProduced = 2 * (++n); cout << valueProduced << endl; cout << n << endl; – This code segment produces the output: 6 3 – Because pre-increment was used
- 26. Console Input/Output • I/O objects cin, cout, cerr • Defined in the C++ library called <iostream> • Must have these lines (called pre- processor directives) near start of file: – #include <iostream> using namespace std; – Tells C++ to use appropriate library so we can use the I/O objects cin, cout, cerr
- 27. Console Output • What can be outputted? – Any data can be outputted to display screen • Variables • Constants • Literals • Expressions (which can include all of above) – cout << numberOfGames << " games played."; 2 values are outputted: "value" of variable numberOfGames, literal string " games played." • Cascading: multiple values in one cout
- 28. Separating Lines of Output • New lines in output – Recall: "n" is escape sequence for the char "newline" • A second method: object endl • Examples: cout << "Hello Worldn"; • Sends string "Hello World" to display, & escape sequence "n", skipping to next line cout << "Hello World" << endl; • Same result as above
- 29. Formatting Output • Formatting numeric values for output – Values may not display as you’d expect! cout << "The price is $" << price << endl; • If price (declared double) has value 78.5, you might get: – The price is $78.500000 or: – The price is $78.5 • We must explicitly tell C++ how to output numbers in our programs!
- 30. Error Output • Output with cerr – cerr works same as cout – Provides mechanism for distinguishing between regular output and error output • Re-direct output streams – Most systems allow cout and cerr to be "redirected" to other devices • e.g., line printer, output file, error console, etc.
- 31. Input Using cin • cin for input, cout for output • Differences: – ">>" (extraction operator) points opposite • Think of it as "pointing toward where the data goes" – Object name "cin" used instead of "cout" – No literals allowed for cin • Must input "to a variable" • cin >> num; – Waits on-screen for keyboard entry – Value entered at keyboard is "assigned" to num
- 32. Prompting for Input: cin and cout • Always "prompt" user for input cout << "Enter number of dragons: "; cin >> numOfDragons; – Note no "n" in cout. Prompt "waits" on same line for keyboard input as follows: Enter number of dragons: ____ • Underscore above denotes where keyboard entry is made • Every cin should have cout prompt – Maximizes user-friendly input/output
- 33. Program Style • Bottom-line: Make programs easy to read and modify • Comments, two methods: – // Two slashes indicate entire line is to be ignored – /*Delimiters indicates everything between is ignored*/ – Both methods commonly used • Identifier naming – ALL_CAPS for constants – lowerToUpper for variables – Most important: MEANINGFUL NAMES!
- 34. Libraries • C++ Standard Libraries • #include <Library_Name> – Directive to "add" contents of library file to your program – Called "preprocessor directive" • Executes before compiler, and simply "copies" library file into your program file • C++ has many libraries – Input/output, math, strings, etc.
- 35. Namespaces • Namespaces defined: – Collection of name definitions • For now: interested in namespace "std" – Has all standard library definitions we need • Examples: #include <iostream> using namespace std; • Includes entire standard library of name definitions • #include <iostream>using std::cin; using std::cout; • Can specify just the objects we want
- 36. Summary 1 • C++ is case-sensitive • Use meaningful names – For variables and constants • Variables must be declared before use – Should also be initialized • Use care in numeric manipulation – Precision, parentheses, order of operations • #include C++ libraries as needed
- 37. Summary 2 • Object cout – Used for console output • Object cin – Used for console input • Object cerr – Used for error messages • Use comments to aid understanding of your program – Do not overcomment