C++ string Class Chapter 6

C++ stringClass Chapter 6

Agenda • String Basics (cin, getline )  • string operations • mixed I/O using >> & getline() • Table Output using setw() • Functions that take string parameters

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

A stringvariable 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;

#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;

#include Libraries should be consistent

string I/O • cin and cout (<< and >> ) work the same • cout<<“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” ???

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

Agenda • String Basics (cin, getline ) • string operations  • mixed I/O using >> & getline() • Table Output using setw() • Functions that take string parameters

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;

String quiz • T/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( ); _______________

Do Lab5 Problems 1-4

Agenda • String Basics (cin, getline ) • string operations • mixed I/O using >> & getline()  • Table Output using setw() • Functions that take string parameters

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"; Console Enter your age: 43 Name (first last): , you don’t look 43.

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"; Console Enter your age: 43 Name (first last):Al Short Al Short, you don’t look 43. Another option:use >> to read the string or strings (instead of getline)

Agenda • String Basics (cin, getline ) • string operations • mixed I/O using >> & getline() • Table Output using setw()  • Functions that take string parameters

#include<iomanip> 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 useoutfile<<setw(4)<< 7 << endl; • Three of the spaces will be blank 7 7 <<left<<

Application of setw( ) problem 6 Produces a table of square roots 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; } Sets column width

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

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

Agenda • String Basics (cin, getline ) • string operations • Table Output using setw() • string I/O using >> & getline() • Functions that take string parameters 

Passing strings to functions • Just 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”);

Finally !!! … THE END 

C++ string Class Chapter 6

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