C++ Chapter 3 Notes

1. C++ Chapter 3 Notes cin Uses and Functions: • cin>> always skips white space when reading data. • cin.get(ch) gets the next character in the input stream and stores it in ch, even if it is a space. • cin.ignore(int value, char value) ignores an integer number of characters/spaces or continues to ignore them until a certain character is reached. (e. g. cin.ignore(80, ‘\n’) ignores 80 spaces or ignores all spaces until the data goes to the next line.) • getline(cin, stringVar) will read an entire line of input into a string variable. If your previous input is a simple data type (i.e. int or char), you must do cin.ignore(80, ‘\n’) before using getline(). • cin.putback(ch) lets you put the last character obtained from the get() function (ch) back into the input stream. • cin.peek() peeks at the next value in the input stream but doesn’t remove it. • If you try to read an invalid value into a variable (i.e. an integer into a character), the program will enter the fail state and all other characters in the input stream will be ignored.

2. Examples • Suppose x is an int, y is a double, and ch is a character. Given the input: 56.8 L4 72 What value (if any) is assigned to x, y, and ch after each statement executes. • cin>>x>>y>>ch; • cin>>y>>ch>>x; • cin>>y; cin.get(ch); cin>>x; • cin.get(ch); cin.putback(ch); cin>>y>>x; • ch=cin.peek(); cin>>y; cin.ignore(50, ‘4’); cin>>x; x=56, y=.8, ch=‘L’ x=4, y=56.8, ch=‘L’ x=input failure, y=56.8, ch=' ' x=input failure, y=56.8, ch=‘5' x=72, y=56.8, ch=‘5'

3. Formatting Output The following manipulators require the header file #include <iomanip> They are all used with cout<<! • setprecision(n) – rounds to n number of decimal places • fixed – outputs doubles in fixed decimal format, as opposed to scientific notation • showpoint – forces the output to show a decimal point with trailing zeros • setw(n) – sets the width of a column • setfill(ch) – fills the empty spaces in the column with a character (ch) • left and right – aligns the output in a column; the default is right

4. Examples Write the code to produce the following outputs: • *****Wazzup!***** • Yo G!$$$$$$$ • This is so cool!.....Oh yeah! This***Rocks! My socks! cout<<setfill(‘*’)<<setw(12)<<“Wazzup!<<setw(5)<<“*”<<endl; cout<<left<<setfill(‘$’)<<setw(12)<<“Yo G!”<<endl; cout<<setfill(‘.’)<<setw(16)<<“This is so cool!”<<setw(13)<<“Oh yeah!” <<endl; cout<<setfill(‘*’)<<setw(4)<<“This”<<setw(9)<<“Rocks!”<<setfill(' ') <<setw(16)<<“My socks!”<<endl;

5. File Input/Output • So far, we have only used the console for input/output. You can also use a file (usually a .txt file). You must include the header file #include <fstream> • You need to declare file stream variables: ifstream fin; ofstream fout; • You must open the files you want to use. For example, if you are getting data from “scores.text” and saving data to “results.text” you would type the following: fin.open(“scores.txt”); fout.open(“results.txt”); If you want the output file to add new info to the end of previous info, instead of replacing it, change the last line to fout.open(“results.txt”, ios::app); • Now you can use fin and fout just like cin and cout! • At the end, you should close your files: fin.close(); fout.close(); You don’t have to use fin and fout. You can call them anything!