Notes

Outline

Simple Data Types: Built-In and User-Defined Additional C++ operators: +=, -=, *=, /= Statement Equivalent Statement i += 5; i = i + 5; pivotPoint *= n + 3; pivotPoint * (n + 3); The Cast Operation Two forms: intVar = (int) floatVar; intVar = int(floatVar); (only works if the data type name is a single identifier) myVar = (unsigned int) someFloat; (the only way for this one)

Working with Character Data Each computer uses a particular character set, two in substantial use today are ASCII and EBCDIC. The vast majority use ASCII. Character Issues: Comparing Characters: if (ch >= ‘a’ && ch <= ‘z’) – islower is preferred usage Converting Digit Characters to Integers: ‘9’ – ‘0’ = 9 Converting to Lowercase and Uppercase: toupper and tolower can help (#include <cctype>)  Accessing Characters Within a String: Use position number, e.g. ch = inputStr[2];

More on Floating-Point Numbers Comparing Floating-Point Numbers: check for an error within some range Underflow and Overflow: Numbers can be too large or too small to be represented. Cancellation Error: problems can occur when arithmetic operations occur on values of wildly different magnitudes: (1 + 0.00001234 – 1) = 0.00001234. For four digits of precision, this doesn’t work, why?

Practical Implications of Limited Precision Limited precision has led to Mercury splashdown in unknown location, delaying the recovery of the spacecraft and the astronaut. Specialized high-tension cables linking a hydroelectric dam to the nearest power distribution point had to be redone due to precision problems. A bank employee stole infinitesimal amounts from a large number of accounts.

User-Defined Simple Types Enumeration Types – C++ allows the user to define a new simple type by listing (enumerating) the literal values that make up the domain of the type. These literal values are identifiers, not numbers, separated by commas. Example: enum Days (SUN, MON, TUE, WED, THU, FRI, SAT);

Enumeration Type Declaration EnumDeclaration enum Name {Enumerator, Enumerator, …}; Enumerator Identifier = ConstIntExpression Legal or Illegal? enum Vowel {‘A’, ‘E’, ‘I’, ‘O’, ‘U’}; enum Places {1st, 2nd, 3rd}; enum Starch {CORN, RICE, POTATO, BEAN}; enum Grain {WHEAT, CORN, RYE, BARLEY, SORGHUM};

More About Enumeration Types Consider the following declaration:    enum Animals {RODENT, CAT, DOG, BIRD, REPTILE, HORSE, BOVINE, SHEEP}; and the following variable declarations:     Animals inPatient;    Animals outPatient; Acceptable assignemnts are    inPatient = DOG;    outPatient = inPatient;    someInt = DOG;    inPatient = Animals(inPatient + 1);

Typical Usage of an Enumeration Type switch (inPatient) {    case RODENT   :    case CAT      :    case DOG      :    case BIRD     : cout << “Cage ward”;                    break;    case REPTILE  : cout << “Terrarium ward”;                    break;    case HORSE    :    case BOVINE   :    case SHEEP    : cout “Barn”;                    break; }

Enumeration Type Input Enumeration types are known only internally to the program, they are input and output indirectly.   string animalName;   cin >> animalName;   switch (toupper(animalName[0]))   {      case ‘R’ : if (toupper(animalName[1] == ‘O’)                    inPatient = RODENT;                 else                    inPatient = REPTILE;                 break;      case ‘C’ : inpatient = CAT;                 break;                  .                  .                  .

Enumeration Type Output Enumeration types are known only internally to the program, they are input and output indirectly.   switch (inPatient)   {      case RODENT :  cout << “Rodent”;                     break;      case CAT    :  cout << “Cat”;                     break;      case DOG    :  cout << “Dog”;                     break;      case BIRD   :  cout << “Bird”;                     break;                  .                  .                  .   }

Using a Value-Returning Function for Input Animals StrToAnimal (/*in*/ string str) {   Animals inPatient;   switch (toupper(str[0]))   {      case ‘R’ : if (toupper(animalName[1] == ‘O’)                    inPatient = RODENT;                 else                    inPatient = REPTILE;                 break;      case ‘C’ : inPatient = CAT;                 break;      case ‘D’ : inPatient = DOG;                 break;                   .                   .                   .      return inPatient;   } }

User-Written Header Files User-defined data types can be useful in more than one program. Declarations can be placed in a header file and included using the #include directive. #include <iostream> looks in the standard include directory #include “months.h” looks in the current directory