QUESTION 5:
- Will this new program compile?
- Will it run?
- Is it correct?
No. The second for loop is trying to use a variable j
that is not defined at that point.
(The first for statement declares a j
than can only be seen within that loop.)
class sameName
{
public static void main ( String[] args )
{
int sumEven = 0;
int sumOdd = 0;
for ( int j = 0; j < 8; j=j+2 )
sumEven = sumEven + j;
System.out.println( "The sum of evens is: " + sumEven );
for ( j = 1; j < 8; j=j+2 ) // "j" can not be seen at this point.
sumOdd = sumOdd + j;
System.out.println( "The sum of odds is: " + sumOdd );
}
}
Here is another version of the program, which is syntactically correct, but is not nicely done.
class foolishTypist
{
public static void main ( String[] args )
{
int sumEven = 0;
int sumOdd = 0;
int j; // Same "j" used for both loops.
for ( j = 0; j < 8; j=j+2 )
sumEven = sumEven + j;
System.out.println( "The sum of evens is: " + sumEven );
for ( j = 1; j < 8; j=j+2 )
sumOdd = sumOdd + j;
System.out.println( "The sum of odds is: " + sumOdd );
}
}
It is best to keep sections of code self-contained. With this (foolish) version, both loops depend on something distant from themselves. Although this program is clear enough, a longer program might be harder to understand. Here, for instance, is a typical hard to understand program:
class foolishTypist
{
public static void main ( String[] args )
{
int sumEven = 0;
int sumOdd = 0;
int j = 0;
int i = 1;
for ( j = 0; j < 8; j=j+2 )
sumEven = sumEven + j;
System.out.println( "The sum of evens is: " + sumEven );
for ( i = 1; i < 8; i=i+2 )
sumOdd = sumOdd + j;
System.out.println( "The sum of odds is: " + sumOdd );
}
}