Wednesday, February 12, 2003

Looping and counting (K&M Chapter 2)

#include <iostream>
#include <string>

// say what standard-library names we use
using std::cin;         using std::endl;
using std::cout;        using std::string;


int main()
{
	// ask for the person's name
	cout << "Please enter your first name: ";

	// read the name
	string name;
	cin >> name;

	// build the message that we intend to write
	const string greeting = "Hello, " + name + "!";

	// the number of blanks surrounding the greeting
	const int pad = 1;

	// the number of rows and columns to write
	const int rows = pad * 2 + 3;
	const string::size_type cols = greeting.size() + pad * 2 + 2;

	// write a blank line to separate the output from the input
	cout << endl;

	// write `rows' rows of output
	// invariant: we have written `r' rows so far
	for (int r = 0; r != rows; ++r) {

		string::size_type c = 0;

		// invariant: we have written `c' characters so far
		// in the current row
		while (c != cols) {

			// is it time to write the greeting?
			if (r == pad + 1 && c == pad + 1) {
				cout << greeting;
				c += greeting.size();
			} else {

				// are we on the border?
				if (r == 0 || r == rows - 1 ||
				    c == 0 || c == cols - 1)
					cout << "*";
				else
					cout << " ";
				++c;
			}
		}

		cout << endl;
	}

	return 0;
}

Working with batches of data (K&M Chapter 3)

#include <iomanip>
#include <iostream>
// #include <ios>
#include <string>

using std::cin;                  using std::setprecision;
using std::cout;                 using std::string;
using std::endl;                 using std::streamsize;

int main()
{
	// ask for and read the student's name
	cout << "Please enter your first name: ";
	string name;
	cin >> name;
	cout << "Hello, " << name << "!" << endl;

	// ask for and read the midterm and final grades
	cout << "Please enter your midterm and final exam grades: ";
	double midterm, final;
	cin >> midterm >> final;

	// ask for the homework grades
	cout << "Enter all your homework grades, "
	        "followed by end-of-file: ";

	// the number and sum of grades read so far
	int count = 0;
	double sum = 0;

	// a variable into which to read
	double x;

	// invariant:
	//     we have read `count' grades so far, and
	//     `sum' is the sum of the first `count' grades
	while (cin >> x) {
		++count;
		sum += x;
	}

	// write the result
	streamsize prec = cout.precision();
	cout << "Your final grade is " << setprecision(3)
	     << 0.2 * midterm + 0.4 * final + 0.4 * sum / count
	     << setprecision(prec) << endl;

	return 0;
}

#include <algorithm>
#include <iomanip>
// #include <ios>
#include <iostream>
#include <string>
#include <vector>

using std::cin;             using std::sort;
using std::cout;            using std::streamsize;
using std::endl;            using std::string;
using std::setprecision;    using std::vector;

int main()
{
	// ask for and read the student's name
	cout << "Please enter your first name: ";
	string name;
	cin >> name;
	cout << "Hello, " << name << "!" << endl;

	// ask for and read the midterm and final grades
	cout << "Please enter your midterm and final exam grades: ";
	double midterm, final;
	cin >> midterm >> final;

	// ask for and read the homework grades
	cout << "Enter all your homework grades, "
	        "followed by end-of-file: ";

	vector<double> homework;
	double x;
	// invariant: `homework' contains all the homework grades read so far
	while (cin >> x)
		homework.push_back(x);

	// check that the student entered some homework grades
	typedef vector<double>::size_type vec_sz;
	vec_sz size = homework.size();
	if (size == 0) {
		cout << endl << "You must enter your grades.  "
		                "Please try again." << endl;	
		return 1;
	}

	// sort the grades
	sort(homework.begin(), homework.end());

	// compute the median homework grade
	vec_sz mid = size/2;
	double median;
	median = size % 2 == 0 ? (homework[mid] + homework[mid-1]) / 2
	                       : homework[mid];

	// compute and write the final grade
	streamsize prec = cout.precision();
	cout << "Your final grade is " << setprecision(3)
	     << 0.2 * midterm + 0.4 * final + 0.4 * median
	     << setprecision(prec) << endl;

	return 0;
}

Last modified: Wed Feb 12 12:28:31 2003