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Answers to Homework 2

Question 2: Declare the following:

an int variable with an initial value of 0int i = 0;

a long variable with an initial value of 10000long l = 10000;

a float variable with an initial value of 3.4float f = 3.4f; // or float f = (float)3.4;

a double variable with an initial value of 34.45double d = 34.45;

a char variable with an initial value of 4char c = (char)4; // I'll accept char c = '4'; or char c = '\0004';

a boolean variable with an initial value of trueboolean b = true;

Question 3: Assume that a = 1 and d = 1.0 and that each expression is independent. What

are the results of the following expressions?

a = 46 / 9;a = 5

a = 46 % 9 + 4 * 4 - 2;a = 1 + 16 - 2 = 15

a = 45 + 43 % 5 * (23 * 3 % 2);a = 45 + 3 * (1) = 48

a = 45 + 45 * 50 % a--;a = 45 + 2250 % a-- = 45 + 0 = 45

a = 45 + 1 + 45 * 50 % (--a);Undefined: (--a) will yield 0, and you can't divide by 0 to do the rest

d += 34.23 * 3 + d++;d = d + (34.23 * 3 + d++) = 104.69

d -= 3.4 * (a + 5) * d++;d = d - (3.4 * (a + 5) * d++) = 1.0 - 20.4 = -19.4

a %= 3 / a + 3;a = a % (3 / a + 3) = 1 % 6 = 1

Question 5: Can different types of numeric values be used together in a computation?

Yes. The types can be mixed through numeric conversions called type casts, which may be

explicit (e.g., "(double)1 / 2") or implicit (e.g., "1 / 2.0" will automatically cast "1" to be of type

double to match the "2.0").

Question 7: Can the following conversions involving casting be allowed? If so, find the

converted result.

char c = 'A';

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i = (int)c;

Legal. The value in "i" will be the character code for 'A'.

boolean b = true;

i = (int)b;

Illegal. You can't convert from type boolean to type int.

float f = 1000.34f;

int i = (int)f;

Legal. The value in "i" will be 1000.

double d = 1000.34;int i = (int)d;

Legal. The value in "i" will be 1000.

int i = 1000;

char c = (char)i;

Legal. The value in "c" will be the character whose Unicode value is 1000.

int i = 1000;boolean b = (boolean)b;

This may be a typo in the text (i.e., using "b" to initialize itself). Either way, it's a typo: youcan't cast an int to be a boolean ("(boolean)i"), and you can't use an object to initialize itself.

Question 8: What is the result of 25 / 4? How would you rewrite the expression if

you wanted the quotient to be a floating-point number?

a. The result is 6.b. You could write it as "25.0 / 4", "25.0 / 4.0", "25 / 4.0", "25f / 4", "25d / 4", "25 / 4f",

"(double)25 / 4", or a host of other ways. The important thing would be to make surethat at least one of the numbers was going to be interpreted as a floating-point value.

Question 10: What does an explicit conversion from a double to an int do with the

fractional part of the double value?

The fractional part is dropped (also known as "truncation").

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Question 13: Show the result of the following Boolean expressions if the result can be

determined:

Expression Result

(true) && (3 > 4) false: the second part can not be true

!(x > 0) && (x > 0) false: either part can be true, but not both

(x > 0) || (x < 0) false if x == 0, true otherwise

(x != 0) || (x ==

0) true: one or the other must be true, regardless of the value of x

(x >= 0) || (x < 0) true: one or the other must be true, regardless of the value of x

(x != 1) == !(x =

1)

Assuming that this is a typo, and the "x = 1" is supposed to be "x ==

1",this must be true, since the two tests are the same.

(If it's not a typo, then the code won't compile.)

Question 15: Write a Boolean expression that evaluates to true if the number is

between 1 and 100 or the number is negative.

( (x > 1) && (x < 100) ) || (x < 0)

Question 17: How do you denote a comment line? How do you denote a comment

paragraph?

a. Comment lines are usually denoted with //.b. Comment paragraphs are denoted with /* and */.

Question 18: Describe compilation errors and runtime errors.

Compilation errors are detected by compilers. They are usually called "syntax errors", and

involve a violation of the grammar of the language.

Runtime errors occur during the execution of the program, and often involve a failure in thelogic of the code (e.g., not handling bad input, running out of memory, etc.).

Programming: page 51, #1

/*

* F2C.java*

* Version:

* $Id$

*

* Revisions:

* $Log$

*/

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/**

* This application computes the Celcius equivalent of

* temperatures input in Fahrenheit.

*

* @author: Rob Duncan

*/

public class F2C

{

/**

* This is the main method for the class

*

* @param args array of string arguments

*

* @return none

*/

public static void main (String[] args)

{

double fahrenheit;

System.out.print( "Please enter the temperature, in degrees

Fahrenheit: " );fahrenheit = MyInput.readDouble();

double celsius = (5.0/9.0) * (fahrenheit - 32);

System.out.println( "That's equal to " + celsius + " degrees

Celsius." );

} // main()

} // F2C