Programming Tutorials

Manipulating Arrays

By: aathishankaran in Java Tutorials on 2007-02-01  

A different type of loop is used in manipulation of arrays. Consider the following example:

PROGRAM_ARRAY_DISP
{
  integer Ctr;
  integer Num_array[5];
  Num_array[0] = 10;
  Num_array[1] = 20;
  Num_array[2] = 30;
  Num_array[3] = 40;
  Num_array[4] = 50;

  for (Ctr=0;Ctr<5;Ctr=Ctr+1)
  {
    display Num_array[Ctr];
  }
}

In this program, the for loop is used to display all the values assigned to the array called Num_array, one by one.

The general form of the for construct is:

for(Expresssion1;Expression2;Expression3)
{
  statement1;
  statement2;
}

• Expression-1: is the initialization expression, usually an assignment. Which is performed once before the loop begins execution.
• Expression-2: is the test expression, exactly like the one used in the while loop, which is evaluated before each iteration of the loop and which determines whether the loop should continue or be terminated.
• Expression-3: is the modifier statement, which changes the value of the variable used in the test. This expression is executed at the end of each iteration after the body of the loop is executed.

The following program sequence using a while construct:

Anynum = 1;
while ( Anynum <100)
{
  display "This line is printed 100 times";
  Anynum = Anynum +1;
}

can be written using a for construct as follows:

for (Anynum =1; Anynum<100; Anynum = Anynum+1)
{
  display "This line is printed 100 times";
}

The choice between while and for is arbitrary, based on which seems clearer. The for is usually appropriate for loops in which the initialization and increment are single statements and logically related, since it is more compact than while and it keeps the loop control statements together in one place.