⚠️ NOTE: You must complete Tut00 before attempting this homework.

In this quick mini homework, we will learn the basics of type and scope by translating Python code into Java.

Here are some Java primitive types (not-Object's):

• An int stores a (signed) integer like -1, 0, or 42
• A char stores a character like 'A', 'b', '7', or '?'
• A double stores a real number like 0.0, 3.1415, or -0.001
• A boolean stores false or true

• When we declare a variable, we have to say what type it is.

  int a = 5; // "make an int called a with value 5"
  int b; // "make an int called b but leave its value undefined for now"

• A variable's value CAN change 🙆

  int b = 5; // "make an int called b with value 5"
  b = 6; // "set the value of b to 6"

• A variable's type CANNOT change 🙅

  int b = 5; // "make an int called b with value 5"
  b = false; // 🚨 COMPILE ERROR: Type mismatch: cannot convert from boolean to int

• A variable must be declared before it is used.

  b = 5;  // 🚨 COMPILE ERRROR: i cannot be resolved to a variable

• In Java, a function must say what type it returns.
  • double foo(...) { ... } returns a double
  • void bar(...) { ... } does not return anything ("returns void")

A scope is a region of code in which variables live

• In Java, a scope is (usually) defined by a pair of curly braces
• OUTER_SCOPE { INNER_SCOPE } OUTER_SCOPE

{
    int i;
    {
        int j;
        // you CAN use i here 🙆
        // you CAN use j here 🙆
    }
    // you CAN use i here 🙆
    // you CANNOT use j here 🙅
}

int i = 0;
i = 1;

i = 1; // 🚨 COMPILER ERROR: i cannot be resolved to a variable
int i = 0;

int i = 0;
{
    i = 1;
    PRINT(i); // 1
}
PRINT(i); // 1

int i = 0;
{
    int i = 1; // 🚨 COMPILER ERROR: Duplicate local variable i
}

{
    int i = 0;
}
i = 1; // 🚨 COMPILE ERRROR: i cannot be resolved to a variable

• A-
  • Complete Tut00
• A
  • In your HW00.java, convert the Python program below into Java (technically, Cow.Java)

def pythag(a, b):
    global D

    result = (a * a + b * b) ** 0.5
    D += result
    return result

A = pythag(3.0, 4.0)
print(A) # 5.0

A = pythag(A, A)
print(A) # 7.0710...

B = (A < 10.0)
if B:
    C = 0
    for i in range(5):
        C += i
    print(C) # 10 (NOT 10.0)
    D += C

assert (D > 20.0)

print(D) # 22.071...

• A+
  • Share a fun fact about yourself in the last question of the HW00 submission page on Glow.

• Please delete the two lines with variable i in them from the starter code once you finish Tut00
• You must translate the program line by line; do NOT try to simplify the program
• You must include the original comments
• Your code must print 10, NOT 10.0
• Use Cow.Java’s ASSERT(...) function instead of Java's assert ... statement. (Java's assert is disabled by default, and it's too easy to forget to enable it)

			class HW00 extends Cow {
public static void main(String[] arguments) {		
				int i = 42 / 0
ASSERT(2 + 2 == 5);
				PRINT(i);
	}
				}

for (int i = 0; i < 10; ++i) {
    ...
}

// "wrapper class"
class HW00 extends Cow {
	
	// global variables
	static int i = 0;
	
	// functions
	static double doStuff(double a) {
		++i;
		return a * a;
	}
	
	// main
	public static void main(String[] arguments) {
		double b = 3.0;
		
		b = doStuff(b);
		PRINT(b); // 9.0
		
		b = doStuff(b);
		PRINT(b); // 81.0
		
		PRINT(i); // 2
	}
	
}

class HW00A extends Cow {
	static double D;

	static double pythag(double a, double b) {
		double result = SQRT(a * a + b * b);
		D += result;
		return result;
	}

	public static void main(String[] arguments) {
		double A = pythag(3.0, 4.0);
		PRINT(A); // 5.0

		A = pythag(A, A);
		PRINT(A); // 7.0710678118654755

		boolean B = (A < 10.0);
		if (B) {
			int C = 0;

			for (int i = 0; i < 5; ++i) {
				C += i;
			}
			PRINT(C); // 10

			D += C;

			ASSERT(D > 20.0);

			PRINT(D); // 22.071067811865476
		}
	}
}