CMSC 202

1. CMSC 202 Computer Science II for Majors

2. Topics • C++ stream input / output • Formatted Output • Project 1 description • Project 1 posted on web

3. Stream I/O in C++ • Stream is a sequence of bytes • C++ introduces objects for I/O • cout which replaces ‘printf’ • cin which replaces ‘scanf’ • cerr : unbuffered standard error output • clog : buffered standard error output • Include iostream header file

4. Stream I/O in C++ …cont • cout • Denotes the output stream (usually console) • Uses insertion operator << to output values to stream • cout << “C++ is better than C”;

5. Stream I/O in C++ …cont • cout Screen << “C++” cout Object Insertion Operator Variable

6. Stream I/O in C++ …cont • cin • Denotes input stream (usually keyboard) • Uses extraction operator >> to input values from stream • Skips white spaces • cin >> number1;

7. Stream I/O in C++ …cont • cin Extraction Operator Object Variable >> cin 45 Key board

8. Example • # include <iostream> • using std :: cout; • using std :: cin; • using std :: endl; • int main() • { • float num1, num2, avg; • cout << “Enter two numbers” ; • cin >> num1; • cin >> num2; • avg = (num1+num2) / 2; • cout << “Average = “ << avg << endl; • return 0; • } • endl is a Manipulator, causes linefeed to be inserted. Just like “/n”

9. Stream I/O operations • Streams are used for File I/O operations • Common file operations • Open file • Process file • Close file • Include fstream header file

10. Stream I/O operations … cont • Streams are typed by operations to be performed on them • ifstream denotes a file used for input • ofstream denotes a file used for output • fstream denotes a file used for both • File I/O used << and >> operators – similar to cin and cout

11. Stream I/O operations … cont • Creating streams • Declare variable for each stream • ifstream Inputfile; • ofstream Outputfile; • Associate stream with a file • Inputfile.open (“file1”); • Outputfile.open (“file2”); • Also possible in single step • ifstream Inputfile (“file1”); • ofstream Outputfile (“file2”);

12. Stream I/O operations … cont #include <fstream> using std::ifstream; using std::ofstream; int main() { ifstream InputFile ("input.txt"); // input stream ofstream OutputFile ("output.txt");// output stream int value = 0; while(InputFile >> value) // similar to cin >> value { OutputFile << "Value =" << value <<endl; } InputFile.close(); OutputFile.close(); return 0; }

13. Formatted Output • Setting field width • Member Function width • cin.width(5); // input only 5 characters • cout.width(5); // sets # of character positions // in which value should be output • Manipulator setw • cin >> setw(5); • cout << setw(5) << ... ;

14. Formatted Output … cont • Setting precision • Manipulators double pi = 3.14159 cout << setprecision(3) <<pi; // 3.142 • Member Function double pi = 3.14159; cout.precision(3); cout << pi; // 3.142

15. Formatted Output … cont

16. Formatted Output … cont • Example #include<iostream> #include<iomanip> using namespace std; int main() { float a,b,c; a = 9; b = 99.099; c = 9.901; cout << "Before formatting:" << endl; cout << "a = " << a << endl; cout << "b = " << b << endl; cout << "c = " << c << endl << endl; cout << "After formatting:" << endl; cout << fixed; cout << setprecision(2); cout << "a = " << setw(7) << a << endl; cout << "b = " << setw(7) << b << endl; cout << "c = " << setw(7) << c << endl; return 0; }

17. Formatted Output … cont • Example Before formatting: a = 9 b = 99.099 c = 9.901 After formatting: a = 9.00 b = 99.10 c = 9.90

18. Formatted Output … cont • Justification • Uses stream manipulators left and right • left : left-justify, padding characters on right • right: right-justify, padding characters on left • cout << left << setw(10) << x ; • cout << right << setw(10) << x ;

19. Project 1 description • Objective : To use string and vector and to experience OOP as user of objects • To use C++ stream operators • Input : Text file • Command line argument • Assume all words are lowercase

20. Project 1 description … cont • Output : an analysis of text in file • Print File name • Total number of words in file • Total number of distinct words • For each alphabet, print # of words, # of distinct words and # of occurrences • Most frequently occurring word

21. Project 1 description … cont • Output … cont 6. Longest Word and # of characters in it • Letter that begins most number of words • Letter that begins most distinct words and # of distinct words with that letter • Letters that do not begin any words

22. Project 1 description … cont • Sample Input (taken from Project description) a very angry and pesky antelope ate all of my angelhair pasta i really really really dislike a very pesky antelope

23. Project 1 description … cont • Sample Output (taken from Project description) linux3[33]% Proj1 p1.dat Processing file "p1.dat" The file contains 21 words. The file contains 15 distinct words. Words that begin with 'a': a:2 angry:1 and:1 antelope:2 ate:1 all:1 angelhair:1 Total words: 9, Distinct words: 7 Words that begin with 'd': dislike:1 Total words: 1, Distinct words: 1

24. Project 1 description … cont • Sample Output …cont Words that begin with 'i': i:1 Total words: 1, Distinct words: 1 Words that begin with 'm': my:1 Total words: 1, Distinct words: 1 Words that begin with 'o': of:1 Total words: 1, Distinct words: 1 Words that begin with 'p': pesky:2 pasta:1 Total words: 3, Distinct words: 2

25. Project 1 description … cont • Sample Output …cont Words that begin with 'r': really:3 Total words: 3, Distinct words: 1 Words that begin with 'v': very:2 Total words: 2, Distinct words: 1 The most frequent word is "really" which occurred 3 times. The longest word is "angelhair" which contains 9 characters. The letter 'a' had the most words - 9 The letter 'a' had the most distinct words - 7 No words begin with the letters b, c, e, f, g, h, j, k, l, n, q, s, t, u, w, x, y, z