Loops

• while ( expression ) statement
  The while statement will execute the statement while the expression is non-zero. It evaluates the expression before each execution of the statement. Termination of the loop is caused by a zero expression value or the execution of a break statement.
• do statement while ( expression ) ;
  The do ... while statement executes statement and evaluates expression. If it is non-zero, do-while reevaluates statement and expression. Termination of the loop is caused by a zero expression value or the execution of a break statement.
• for ( expression1 ; expression2 ; expression3 ) statement
  The for statement controls repeated execution of the statement. expression1 is evaluated before the loop. expression2 is evaluated before each execution of the statement. If it is non-zero, the statement is evaluated. If it is zero, the loop is terminated. After each execution of the statement, expression3 is evaluated before the reevaluation of expression2. If expression1 or expression3 are missing, nothing is evaluated at the point they would be evaluated. If expression2 is missing, it is the same as substituting the value 1 for expression2. The following is equivalent code for the for statement:

  expression1; while (expression2) { statement; expression3; }

  Again, termination of the loop can be caused by the execution of a break statement.

The following example prints the squares of the numbers 1 to 10 in reverse order. It is implemented in three different ways to illustrate the use of the different kinds of loops:

LC Session

lc> i = 10; 
$44 = 10
lc> while (i > 0) { print(i^2, " "); i--; } print("\n");
100 81 64 49 36 25 16 9 4 1 
lc> for (i = 10; i > 0; i--) print(i^2, " "); print("\n");
100 81 64 49 36 25 16 9 4 1 
lc> i = 10;
$45 = 10
lc> do { print(i^2, " "); i--; } while (i > 0); print("\n");
100 81 64 49 36 25 16 9 4 1 
lc>