Java Reference
In-Depth Information
Java syntax: for-loop for processing a range of integers b..c
for ( int i= b; i <= c; i= i + 1) {
Process i;
Purpose : To perform the sequence of statements “Process b ; Process b+1 ;
...; Process c ;”. Here, “Process i ” can be any statement sequence that
refers to variable i . Also, b and c can be any integer expressions such that
b<=c+1 . If b = c+1 , then no integers are processed.
the following sequence, the second declaration is illegal, since variable b is
declared in the first line. But the third line, the assignment to b , is legal.
// A legal initializing declaration
int b= 45;
// An illegal declaration, since b is already declared
int b= 61;
// A legal assignment
b= b + 2;
Processing a range of integers
This section need not be read at this time. It is presented here so that instructors
who want to introduce loops early can do so. If you are not interested in study-
ing loops at this point, skip this section.
At times, we want to write a program segment to process a range of integers.
Here are some examples of tasks that we might want to perform:
• Add the squares of the integers in the range 1..100 (i.e. the integers 1 , 2 ,
…, 100 ).
• Determine whether some integer in the range 2..n divides an integer k .
• Find the first integer in the range 100.. (i.e. the first integer ≥ 100 ) that is
a power of 2 (i.e. can be written in the form 2 k for some k ).
• Find the number of times the letter 'e' appears in String s (this requires
processing the possible indices 1..(s.length-1) of s ).
Program segments to process a range of integers are usually written using a
loop , and often with what is called a for-loop . Chapter 7 covers loops in detail;
here, we provide just enough information to allow you to write simple loops to
process a range of integers.
Suppose you want to implement the following sequence of statements,
which stores in int variable x the sum of the integers in the range 2..200 . Here
is one way to do it:
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