Elements of a simple C++ program

• Documentation : Comment using //
• // : for rest of line
• /* start of any length comment and end */
• Your name
• Class Period
• Due date of assignment
• Program description
• Variable dictionary of all variables declared and used by this module
• Description of interface to other modules
• Inclusion of libraries -- #include <iostream.h>
• Name of "main" function : main()
• Precede by int
• Precede by void

• Use brackets around code
• { indicates beginning of code segment
• } indicates end of code segment
• Print or display text : cout << "message";
• Terminate statement with ;
• Use << with cout
• (Use >> with cin)
• Tabs : \t
• Carriage return : \n
• Return value to environment : return 0;

Programming Style

• Document!!
  Program descriptions
  Use of variables
• Use whitespace
  blank spaces around operators (+, =, ...)
  blank lines "around" sections of code
  More to come about this in next chapter...

Program Format

• #include directive
• using namespace
• main
• code in the scope of main
• end of main

Variable declaration

1. Variables must be declared before they can be used.
2. Type followed by name of variable (identifier)
   Types are reserved words such as int
3. Identifiers
• Consist of letters, digits and _
• Begin with letter or _ (not good idea)
• Case sensitive (a1 and A1 are different)
• Cannot be a keyword or reserved word
• No limit to length. For compatibility use 31 characters
• Use meaningful names
• All caps indicates a constant
• Beginning with _ indicates a system defined variable
4. Declarations
   • Integer declaration
     int length, width;
     char shirt_size
     
   • Placement of variable declaration : almost anywhere
   • For now, place them immediately after {
   • Results in storage allocation from RAM

Types can be:

• Integer is 4 bytes -2,147,483,647 to +2,147,483,647. int
• Short integer is 2 bytes -32,767 to 32,767. short int or short
• Long integer is usually 4 bytes. long int or long
• Floating point is 4 bytes. 10^-38 to 10³⁸. float
• Double is 8 bytes. 10^-308 to 10³⁰⁸. double
• Long double is 10 bytes. 10^-4932 to 10⁴⁹³². long double
• Character is 1 byte, 256 ASCII values. char
• Boolean is 1 byte. true or false. bool
• C++ string Class
  #include <string>
  string myTeam;
  myTeam = "The Cleveland Browns";

• 5 is an integer, '5' is a character, and "5" is a string
• Characters (i.e., can only hold a single character
• Strings can hold 1 or more characters
• The end of line character looks like 2 characters to us, but is interpreted as one '\n'.
• The tab character is '\t'.
• There are other special backslash characters, but the tab and newline are used frequently. (See Table 2-2 of your text)
• Use single quotes around a single letter
• Single letters: 'A', '1', '-'
• Single letters include escape characters: '\n' and '\t'
• The null string is represented as "" but really has a hidden character in it known as the end of string
• To use strings, you must use the include directive and the string header
  #include <string>
• \ is an escape character and can be used to get s ' \ "
  \' \\ \"
• Casting can be done between characters and numerics
• char c=68.5 assigns the character at ascii code 68 to c - the letter 'D'
• int i ='D' assigns the integer 68 to i
• int j = 2 + 'a' adds 2 to 97 which is the ascii charcter code for 'a'. Thus 99 is assigned to j
• Such implicit type casting is not recommended as it is difficult to read and figure out. If you use it, DOCUMENT IT!

• 5L is a long integer which currently holds the same values as an integer
• 5LL is a very long integer and gives you a larger range
• float and double permit decimal numbers
• There is a mathematical difference between 5 and 5.0
• Computers have a physical limit on the number of decimal places
• Scientific notation are number such as 3.76E2 which is 3.7 time 10 squared or 3.7 X 100 or 370

• General format: Variable = Expression
• perimeter = length + length + width + width;
• Semantics
• evaluate the right hand side (rhs)
• use operator precedence
• use type rules for operators
• possibly typecast result to the lhs type
• place result in memory for variable
• Potential error
• Incorrect types for operators
• Division by 0
• Typecasting results in loss of precision
• Not enough room in memory (type mismatch)

• You can initialize a variable when you declare it
• If not initialized, whatever is it RAM at that location is used
• int i=0;
• int i=1, j=0;
• double x=3.14;

Named Constants

• A permanent data value that cannot be changed
• General format: const type identifier = value ;
• Example:
  const double PI = 3.14159;
• Identifier is usually in all CAPS