Assignment #2 solution

1.cpp

// #1. Ex 5.2 question 9 solution

#include <iostream>
#include <iomanip>
#include <cmath>

using namespace std;

int
main(void)
{
	int i;
	double e, e1, fact;

	e = 1;		// 1/0!
	fact = 1;		// 1!
	e1 = e+1/fact;	// 1/0! + 1/1!
	i = 2;
	while(fabs(e1-e) >= 10e-9){
		e = e1;
		fact *= i;
		e1 += 1/fact;
		i++;
	}
	cout << "e = " << fixed << setprecision(8) << e1 << endl;

	return 0;
}

1alt.cpp

// #1. Ex 5.2 question 9 solution (optimized)

#include <iostream>
#include <iomanip>
#include <cmath>

using namespace std;

int
main(void)
{
	int i;
	double e, t, fact;

	fact = 1;
	e = 1;
	i = 1;
	do {
		fact *= i;
		t = 1/fact;
		e += t;
		i++;
	} while(t >= 10e-9);
	
	cout << "e = " << fixed << setprecision(8) << e << endl;

	return 0;
}

2.cpp

// #2 solution

#include <iostream>

using namespace std;

int
main(void)
{
	int x;

	do {
		cout << "Enter x: ";
		cin >> x;
	} while (x < 10 || 50 < x);

	for(int i = 0; i < x; i++){
		for(int j = 0; j < i+1; j++)
			cout << "*";
		cout << endl;
	}
	return 0;
}

3.cpp

// #3 solution

#include <iostream>

using namespace std;

int
main(void)
{
	int op, left, right, answer, guess, score, nques, again;
	bool correct;
	double avgscore;
	
	const int ADD = 1, SUB = 2, MUL = 3, DIV = 4;
	
	score = nques = 0;
	for(;;){
		cout << "[" << ADD << "=add, "
			<< SUB << "=subtract, "
			<< MUL << "=multiply, "
			<< DIV << "=divide]: ";
		cin >> op;
		if(op != ADD && op != SUB && op != MUL && op != DIV){
			cout << "invalid input; try again" << endl;
			continue;
		}
		cout << "Enter the two operands: ";
		cin >> left >> right;
		if(op == DIV && right == 0){
			cout << "cannot divide by zero; try again" << endl;
			continue;
		}
		
		switch(op){
		case ADD:
			answer = left + right;
			break;
		case SUB:
			answer = left - right;
			break;
		case MUL:
			answer = left * right;
			break;
		case DIV:
			answer = left / right;
			break;
		default:	// unreachable
			cout << "internal error" << endl;
			return 2;
		}
		correct = false;
		for(int i = 0; i < 3; i++){
			cout << "Enter your answer: ";
			cin >> guess;
			if(guess == answer){
				correct = true;
				score++;
				break;
			}
			score--;
		}
		if(!correct)
			cout << "The correct answer is " << answer << endl;
		nques++;
		
		cout << "[1=continue, 0=quit]: ";
		cin >> again;
		if(again == 0)
			break;
	}
	
	cout << "Number of questions tested: " << nques << endl;
	cout << "Your overall score: " << score << endl;
	
	avgscore = score/double(nques);
	if(avgscore > 0.5)
		cout << "Great" << endl;
	else if(avgscore < 0)
		cout << "Poor" << endl;
	else
		cout << "Fine" << endl;
	
	return 0;
}