Chapter 3. Expressions and Interactivity

1. Chapter 3. Expressions and Interactivity CSC125 Introduction to C++

2. Formatting Output • Ex. Input 6 integers n1,n2,n3,n4,n5,n6 in the range of [0,10000], and display them on the screen as a table shown below: n1 n2 n3 n4 n5 n6 • Cout uses just the number of spaces needed to print each number

3. Formatting output • A stream manipulator • setw(aNumber) : establish print fields of a specified width. • aNumber is the field width for the value immediately following it. Minimum number of spaces to print the value in.

4. Formatting Output • #include <iomanip> • Cout goes back to its default method of printing • Any number larger than the minimum will cause cout to override the setw value.

5. Formatting Output • The field width of a floating-point number includes a position for the decimal point • The field width of a string includes all characters in the string, including spaces • These values printed in the field are right-justified by default.

6. Formatting Output • Right justified. double x=146.789, y=24.23,z=1.2; cout<<setw(10)<<x<<endl; cout<<setw(10)<<y<<endl; cout<<setw(10)<<z<<endl; • Left justified. double x=146.789, y=24.23,z=1.2; cout<<left<<setw(10)<<x<<endl; cout<<setw(10)<<y<<endl; cout<<setw(10)<<z<<endl;

7. The setprecision(aNumber) Manipulator • Floating-point values may be rounded to a number of significant digits • You can control the number of significant digits with which floating-point values are displayed. • Unlike setw(), setprecision manipulator remains in effect until it is changed to some other values.

8. Fixed vs Scientific • Stream manipulator, fixed, forces cout to print the digits in fixed-point notation. float f1=3.2472, f2=12.9e3; double d=327.815; cout<<fixed<<f1<<endl<<f2<<endl; cout<<scientific<<d<<endl<<f2<<endl; cout<<setprecison(2); cout<<fixed<<f1<<endl<<f2<<endl; cout<<scientific<<d<<endl<<f2<<endl;

9. Fixed vs Scientific • setprecision(x): when used with fixed or scientific, print floating-point value using x digits after the decimal. Without fixed or scientific, print floating-point value using x significant digits

10. showpoint • By default, floating-point numbers are not displayed with trailing zeroes • Six significant digits are specified. • showpoint manipulator

11. Happy Moon Festival

12. Formatted Input • Can format field width for use with cin • Useful when reading string data to be stored in a character array: const int SIZE = 5; char fName[SIZE]; cout << "Enter your name: "; cin >> setw(SIZE) >> fName; • cin reads one less character than specified in setw() directive

13. Procedural and Object-Oriented Programming • Procedural programming: focus is on the process. Procedures/functions are written to process data. • Object-Oriented programming: focus is on objects, which contain data and the means to manipulate the data. Messages sent to objects to perform operations.

14. cin.getline() • To read an entire line of input, use cin.getline(): const int SIZE = 81;char address[SIZE]; cout << "Enter your address: "; cin.getline(address, SIZE); • cin.getline takes two arguments: • Name of array to store string • Size of the array

15. Reading a charcter • To read a single character: • Use cin: char ch; cout << “Press any key to continue"; cin >> ch; Problem: will skip over blanks, tabs, <CR> • Use cin.get(): cin.get(ch); Will read the next character entered, even whitespace

16. Mixing cin >> and cin.get() • Mixing cin and cin.get() in the same program can cause input errors that are hard to detect

17. How to solve it? • To skip over unneeded characters that are still in the keyboard buffer, use cin.ignore(): cin.ignore(); // skip next char cin.ignore(n, c); // skip the next // n char. or until a //character c is met.