Tcl - Loops
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.
