CS 211:
Introduction to Computer Programming II

	Instructor: Brian M. Dennis
	Teaching Assistants:
	Tom Lechner, Bin Lin
	http://www.cs.northwestern.edu/~bmd/cs211/

Logical Operators

	int fib(int n) {
	if (n < 0) return 0;
	if (n == 0) return 0;
	if (n == 1) return 1;
	return fib(n-1) + fib(n-2);
	}

Logical Operators

	int fib(int n) {
	if ((n < 0) || (n == 0)) return 0;
	if (n == 1) return 1;
	return fib(n-1) + fib(n-2);
	}

Logical Operators

	// (0 <= x) && (x < 100)
	#include <cmath>
	double safe_invert(double val) {
	double z = 0.0;
	bool foo = false;
	foo = ((0.0 != val) && (z = 1.0 / val));
	return z;
	}

Unary Operators

	// ! is the unary logical negation operator
	!((0 <= x) && (x <= 100))
	è
	(!(0 <= x)) || (!(x <= 100))
	è
	(x < 0) || (x > 100)

If statement

	int fib(int n) {
	if (n < 0) return 0;
	if (n == 0) return 0;
	if (n == 1) return 1;
	return fib(n-1) + fib(n-2);
	}

If/else statement

	int fib(int n) {
	if ((n < 0) || (n == 0)) return 0;
	if (n == 1)
	return 1;
	else
	n = n – 1;
	return fib(n-1) + fib(n-2);
	}

If/elseif/else statement

	int fib(int n) {
	if (n < 0) {
	return 0;
	} else if (n == 0) {
	return 0;
	} else if (n == 1) {
	return 1;
	} else {
	n = n – 1;
	return fib(n-1) + fib(n-2);
	}
	}

switch statement

	int fib(int n) {
	int res = 0;
	switch(n) {
	case "blah":
	res = 0;
	case 1.0:
	res = 1;
	break;
	case res:
	default:
	res = fib(n-1) + fib(n-2);
	}
	return res;
	}

do/while statement

	int fib_iter_helper(int a, int b, int count);
	int fib_iter(int n) {
	return fib_iter_helper(1, 0, n);
	}
	int fib_iter_helper(int a, int b, int count) {
	if (count == 0) return b;
	return fib_iter_helper(a + b, a, count - 1);
	}

do/while statement

	int fib_pure_iter(int n) {
	int a = 1;
	int b = 0;
	int old_a;
	do {
	old_a = a;
	a = a + b;
	b = old_a;
	n = n - 1;
	} while (0 < n);
	return b;
	}

while statement

	int fib_pure_iter(int n) {
	int a = 1;
	int b = 0;
	int old_a = 1;
	while (0 < n) {
	old_a = a;
	a = a + b;
	b = old_a;
	n = n - 1;
	}
	return b;
	}

for statement

	int fib_pure_iter(int n) {
	int a = 1;
	int b = 0;
	int old_a = 1;
	for (int i = 0; i < n; i = i + 1)
	{
	old_a = a;
	a = a + b;
	b = old_a;
	}
	return b;
	}

for statement

	int fib_pure_iter(int n) {
	int a, b, old_a;
	for (a = 1, b = 0, old_a = 1;
	0 < n;
	n = n - 1
	)
	{
	old_a = a;
	a = a + b;
	b = old_a;
	};
	return b;
	}

Parameter passing

	void swap(int x, int y) {
	int old_x = x;
	x = y;
	y = old_x;
	}
	int main() {
	int x = 10, y = 20;
	swap(x, y);
	cout << "x: " << x;
	cout << " y: " << y;
	cout << "\n";
	return 1;
	}

Parameter passing

	void swap(int& x, int &y) {
	int old_x = x;
	x = y;
	y = old_x;
	}
	int main() {
	int foo = 10, bar = 20;
	swap(x, y);
	cout << "x: " << x;
	cout << " y: " << y;
	cout << "\n";
	return 1;
	}

That’s a Wrap

	Takeaways
		Logical operators
		Conditional/selection
		Iteration constructs
		Call by reference
	Reading
		2.1 – 2.7,
		2.13 – 2.20
	Get HW2 turnin instructions