Exercise 4.x2: The for statement in languages such
as Java is sufficiently general that not all four components are
needed for some applications. As an example, complete the LeftDigit.java
program shown below by filling in two of the four blanks, leaving the other two
empty. The goal is that you should be able to compile and test the
program as follows:
javac LeftDigit.java java LeftDigit 314 -314 5 -5 10 -10 0
and receive the following output:
314: 3 -314: -3 5: 5 -5: -5 10: 1 -10: -1 0: 0
The program you are to complete follows:
public class LeftDigit {
public static int leftDigit(int n){
for(__________; __________; __________)
__________;
return n;
}
public static void main(String[] args){
for(String arg : args)
System.out.println(arg + ": " + leftDigit(Integer.parseInt(arg)));
}
}
Exercise 4.x3: Complete the Fib.java
program shown below by filling in the contents of the
switch statement subject to the following constraints:
(1) You should use only one return statement. (2) You
should not modify any code outside the switch statement.
(3) Your procedure should calculate Fibonacci numbers using a
tree-recursive process. You should be able to compile and test
as follows:
javac Fib.java java Fib 0 1 2 3 4 5 6 7 8 9
and receive the following output:
0: 0 1: 1 2: 1 3: 2 4: 3 5: 5 6: 8 7: 13 8: 21 9: 34
The program you are to complete follows:
public class Fib {
public static int fib(int n){
switch(n){
}
}
public static void main(String[] args){
for(String arg: args)
System.out.println(arg + ": " + fib(Integer.parseInt(arg)));
}
}
Exercise 4.x4: The following Java program contains several
different variables that are named n. Show your
knowledge of scoping rules by renaming each of the variables to a
distinct name, such as n1, n2, or
n3, while making sure that the meaning of the program is
unchanged.
public class Scoping {
public static void main(String[] args){
int before = n, n = 42, after = n;
foo(before);
foo(after);
bar();
}
private static void foo(int n){
System.out.println(n);
}
private static void bar(){
System.out.println(n);
}
private static int n = 17;
}
Exercise 4.x5: Page 111 of the textbook mentions that languages differ with regard to whether a procedure's parameters have the same scope as local variables defined in the procedure's body or whether they constitute an outer scope wrapped around the procedure body. Jay follows the example of Java in using the same scope for the parameters and the body. How would the definition of typingm on page 115 need to be changed in order to make Jay instead be like Algol 60, with the parameters bound in a distinct scope just outside the scope for the procedure body?