there may be a situation, where you need to execute a block of code several number of times. in general, statements are executed sequentially: the first statement in a function is executed first, followed by the second, and so on.
programming languages provide various control structures that allow for more complicated execution paths.
a loop statement allows us to execute a statement or group of statements multiple times and following is the general form of a loop statement in most of the programming languages −
tcl language provides the following types of loops to handle looping requirements.
| sr.no. | loop type & description |
|---|---|
| 1 |
while loop
repeats a statement or group of statements while a given condition is true. it tests the condition before executing the loop body. |
| 2 |
for loop
executes a sequence of statements multiple times and abbreviates the code that manages the loop variable. |
| 3 |
nested loops
you can use one or more loop inside any another while, for or do..while loop. |
loop control statements
loop control statements change execution from its normal sequence. when execution leaves a scope, all automatic objects that were created in that scope are destroyed.
tcl supports the following control statements.
| sr.no. | control statement & description |
|---|---|
| 1 |
break statement
terminates the loop or switch statement and transfers execution to the statement immediately following the loop or switch. |
| 2 |
continue statement
causes the loop to skip the remainder of its body and immediately retest its condition prior to reiterating. |
the infinite loop
a loop becomes infinite loop if a condition never becomes false. the while loop is traditionally used for this purpose. you can make an endless loop by leaving the conditional expression as 1.
while {1} {
puts "this loop will run forever."
}
when the conditional expression is absent, it is assumed to be true. tcl programmers more commonly use the while {1} construct to signify an infinite loop.
note − you can terminate an infinite loop by pressing ctrl + c keys.