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C++ string ClassChapter 6

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Agenda

String Basics (cin, getline ) string operations

mixed I/O using >> & getline()

Table Output using setw()

Functions that take string parameters

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What’s a string?

A string is a sequence of letters in quotes“Hello” “C++ is fun!” “” (empty string)

cout<<“This is a string literal”<<endl;

ofstream fout(“accnts.txt”);

this is also a string literal

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A string variable stores strings

string s1; // empty string

string s2 = “Hello World”;

string s3(60, ‘*’);

//s3 contains 60 asterisks

s1=s2; //copy string s2 into s1

cout<<“String s1 holds ”<<s1<<endl;

cout<<s3<<endl;

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#include <string> to use string

string is a class that was created in ’98 to improve on C-strings (tedious arrays of char)

The whole C++ standard was revised as well

Keep using these post ’98 libraries :

#include <iostream>

#include <string>

using namespace std;

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#include Libraries should be consistentPre ’98 Standard Post ’98 Standard

<iostream.h>

<fstream.h>

<iomanip.h>

<math.h>

<stdlib.h>

<string> new C++ string

<string.h> old C-string

<iostream>

<fstream>

<iomanip>

<cmath>

<cstdlib>

<string> new C++ string

<cstring> old C-string

You must also add

using namespace std;

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string I/O

cin and cout (<< and >> ) work the samecout<<“Enter two strings”<<endl;

cin>>s1>>s2; // whitespace separates strings

You type Gong Li

You get s1 s2

Problem: How do you get s1 to hold “Gong Li” ???

Gong Li

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string input with getline( ) problem 2

getline( ) Reads everything until a ‘\n’ is found

getline(cin, s1);

getline(cin, s2);

You type

Gong Li

Quoth the Raven, “Nevermore!”

You get s1 s2

Gong Li Quoth the Raven, “Nevermore!”

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Agenda

String Basics (cin, getline )

string operations mixed I/O using >> & getline()

Table Output using setw()

Functions that take string parameters

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C++ string operations problem 4

Length of a C++ string can be found as : s.length(); // returns length of s

C++ strings can be compared using relational operators like :

if(s2 < s5) //… if(name == “Jones”)

C++ strings can be concatenated and appended using the + and the += operators :

string s6 = s5 + “HIJK”; s2 += s5;

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String quizT/F (“Salty” < “Sweet”)T/F (“aardvark” == “Aardvark”)T/F (“John” > “john”)

What does full hold?string last=“Woods”, first = “Tiger”, full;a) full = first + last; _______________b) full = first + “ “ + last; _______________c) full = last + “, ” + first; _______________

What does k hold?int k = first.length( ); _______________

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Do Lab5 Problems 1-4

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Agenda

String Basics (cin, getline )

string operations

mixed I/O using >> & getline() Table Output using setw()

Functions that take string parameters

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Warning—weird behavior mixing >> and getline( ) problem 5

string name; int age; cout << "Enter your age: "; cin >> age; cout << "Name (first last): "; getline (cin, name); cout << name << ", you don't look " << age << ".\n";

Enter your age: 43

Name (first last):

, you don’t look 43.

Console

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Warning—weird behavior mixing >> and getline( ) problem 5

string name; int age; cout << "Enter your age: "; cin >> age; does not remove enter key (‘\n’) cout << "Name (first last): "; cin.ignore (80, '\n'); ignores ‘\n’ left by cin>> getline (cin, name); cout << name << ", you don't look " << age << ".\n";

Another option: use >> to read the string or strings (instead of getline)

Enter your age: 43

Name (first last):Al Short

Al Short, you don’t look 43.

Console

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Agenda

String Basics (cin, getline )

string operations

mixed I/O using >> & getline()

Table Output using setw() Functions that take string parameters

Slide 17

Creating Space in Output The setw function specifies the number of

spaces for the next item Applies only to the next item of output

Example: To print the digit 7 in four spaces use outfile<<setw(4)<< 7 << endl; Three of the spaces will be blank

7 7

<<left<<

#include<iomanip>

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int n;cout << " N sqrt(N)" << endl;cout << "-----------" << endl;cout << fixed << showpoint<<setprecision(3);for (n=1; n<=10; n++) { cout << setw(2) << n; cout << setw(8) << sqrt(n); cout << endl; }

Application of setw( ) problem 6Produces a table of square roots

Sets column width

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const double RATE = 4.55; int tutor; int hours; string name; ofstream fout("output.txt");

for (tutor=1; tutor<=3; tutor++) { cout << "Tutor's name and hours worked: "; cin >> name >> hours; fout << fixed << showpoint << setprecision(2); fout << left<< setw(15) << name

<< right << setw(10)<< hours << setw(10) << hours*RATE << endl; }

Notice

Left and right

justification

Application of setw( ) problem 7Produce a formatted table of strings and numbers

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Do 5,6,7 (skip 8 for now) and 9

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Agenda

String Basics (cin, getline )

string operations

Table Output using setw()

string I/O using >> & getline()

Functions that take string parameters

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Passing strings to functionsJust like other parameters, strings can be passed to and returned from functions

string AddJunior(string name)

{

name=name+”, Jr.”;

return name;

} FUNCTION CALL:

string son;

son=AddJunior(“Hank Williams”);

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Finally !!! … THE END