c++ for engineers and scientists second edition chapter 7 completing the basics

C++ C++ forfor Engineers and ScientistsEngineers and Scientists

Second EditionSecond Edition

Chapter 7Completing the Basics

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ObjectivesObjectives

• Exception Handling• The string Class• Character Manipulation Methods• Input Data Validation• Namespaces and Creating a Personal Library• Common Programming Errors

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Exception HandlingException Handling

• Exception: a value, variable, or object that contains information about the error that occurred

• Exception handler: code designed to deal with exceptions

• Throwing an exception: the process of generating and passing an exception at the point where the error was detected

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Exception Handling (continued)Exception Handling (continued)

• Two basic types of errors, caused by– Inability to obtain a required resource

– Flawed data

• Catch an exception: receive a thrown exception and process it

• Try and catch keywords are used for throwing and catching exceptions

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Exception Handling (continued)Exception Handling (continued)

• try keyword starts the exception handling block of code

• Statements that may throw an exception are placed within the braces

• One or more catch blocks follow the try block• Each catch block catches a unique exception

type, identified in parentheses• At least one catch block is required for a try

block

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Exception Handling (continued)Exception Handling (continued)

Syntax:

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Exception Handling (continued)Exception Handling (continued)

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The The stringstring Class Class• Class: a user-created data type that defines a

valid set of data values and a set of operations that can be used on them

• Object: storage area declared for a class• string class permits string literals• String literal: any sequence of characters

enclosed in double quotation marks; also called string value, string, constant

Figure 7.1 The storage of a string as a sequence of characters.

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The The stringstring Class (continued) Class (continued)

• string class provides functions for declaring, creating, and initializing a string

• Methods: functions in a class• Constructor: the method which creates and

initializes a string object• string header file is required to use the string class

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The The stringstring Class (continued) Class (continued)

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The The stringstring Class (continued) Class (continued)

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The The stringstring Class (continued) Class (continued)

• Character positions within a string are numbered starting with zero

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The The stringstring Class (continued) Class (continued)

• Strings can be input from the keyboard and displayed on the screen using cout, cin, and getline

• getline continuously accepts and stores characters from the keyboard until the terminating key is pressed

• If the last argument is omitted, the Enter key will terminate the inputSyntax:

getline(cin, strObj, terminatingChar)

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The The stringstring Class (continued) Class (continued)

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The The stringstring Class (continued) Class (continued)

• Using cin and getline inputs together in the same program may cause problems

• cin accepts the input, but leaves the newline code from the Enter key in the buffer, which will be picked up by the getline as the end of its input

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The The stringstring Class (continued) Class (continued)

• Three possible solutions to this problem:– Do not use cin and getline inputs in the

same program

– Follow the cin input with cin.ignore()

– Accept the Enter key into a character variable and then ignore it

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The The stringstring Class (continued) Class (continued)

• string class provides many methods for manipulating strings, including– length: returns the length of the string– at: returns the character at the specified index– compare: compares two strings– empty: tests if the string is empty– erase: removes characters from the string– find: returns the index of the first occurrence of

a string in an object

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The The stringstring Class (continued) Class (continued)

• string class methods (continued):– insert: inserts one string into another string at

the specified index– replace: replaces characters in an object at

the specified index– substr: returns a portion of a string– swap: swaps characters in a string with a

specified object

• Concatenation operator (+) combines two strings

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The The stringstring Class (continued) Class (continued)

• All relational operators may be used to compare strings; ASCII or UNICODE code values are used for comparison

Figure 7.5 The initial strings used in Program 7.6.

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The The stringstring Class (continued) Class (continued)

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The The stringstring Class (continued) Class (continued)

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The The stringstring Class (continued) Class (continued)• Example: Inserting characters in a string

string str = “This cannot be”;

str.insert(4, “ I know”);

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The The stringstring Class (continued) Class (continued)

• Example: Replacing characters in a string

str.replace(12, 6, “to”);

str += “ correct”;

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The The stringstring Class (continued) Class (continued)

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Character Manipulation MethodsCharacter Manipulation Methods

• Character manipulation methods require the header file string or cctype

• character class provides methods for character manipulation, including– Character type detection: isalpha, isalnum, isdigit, isspace, isprint, isascii, isctrl, ispunct, isgraph, isupper, islower

– Character case conversion: toupper, tolower

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Character Manipulation Methods Character Manipulation Methods (continued)(continued)

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Character Manipulation Methods Character Manipulation Methods (continued)(continued)

• Basic character I/O methods, requiring the header file cctype, include– cout.put: put a character on the output stream– cin.get: extract a character from the input

stream– cin.peek: assign the next character from the

input stream to a variable without extracting it– cin.putback: pushes a character back onto

the input stream– cin.ignore: ignores input characters

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Character Manipulation Methods Character Manipulation Methods (continued)(continued)

• When a character is requested after the user has already input some other data, get() method may pick up the Enter key instead of the new data

• Two ways to solve this problem:– Use a cin.ignore() after the cin.get()– Accept Enter key and do not process it

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Character Manipulation Methods Character Manipulation Methods (continued)(continued)

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Input Data ValidationInput Data Validation

• User-input validation includes checking each entered character to ensure it is the expected data type

• Can accept user input as a string, and then check each character for proper typeExample: input of an integer number

– Data must contain one or more characters

– If the first character is a + or -, there must be at least one digit

– Only digits from 0 to 9 are acceptable

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Namespaces and Namespaces and Creating a Personal LibraryCreating a Personal Library

• Namespaces provide the ability to group a set of classes, objects, or functions under a nameSyntax:

namespace name

{

functions and/or classes in here

} // end of namespace

• A file can contain more than one namespace

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Namespaces and Creating Namespaces and Creating a Personal Library (continued)a Personal Library (continued)

• To use the namespace file, add a preprocessor directive containing the namespace path to the program Example:

#include <c:\\mylibrary\\dataChecks>

using namespace dataChecks;

• If more than one namespace is in the file, only the requested namespace will be loaded

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Common Programming ErrorsCommon Programming Errors

• Failure to include the string header file when using string class objects

• Failure to remember that the newline character, ‘\n’, is a valid data input character

• Failure to convert a string class object using the c_str() method when converting to numerical data types

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SummarySummary

• String literal: any sequence of characters enclosed in double quotation marks

• string class can be used to construct a string• string class objects are used when

comparing, searching, examining, or extracting a substring, or replacing, inserting, or deleting characters

• cin object terminates input when a blank is encountered

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Summary (continued)Summary (continued)

• getline() method can be used for string class data input

• cout object can be used to display string class strings