§12 循环101－while循环

 

                        §12   循环101－while循环

            While和for具有一定的可替换性。语法如下：

• while test body

continue终止当次循环，break退出整个循环。

            注意while之后要用大括号来括住，用引号的话会导致只进行一次替换，导致无限循环。

 

实例：

 

set x 1

 

# This is a normal way to write a Tcl while loop.

 

while {$x < 5} {

    puts "x is $x"

    set x [expr {$x + 1}]

}

 

puts "exited first loop with X equal to $x\n"

 

# The next example shows the difference between ".." and {...}

# How many times does the following loop run?  Why does it not

# print on each pass?

 

set x 0

while "$x < 5" {

    set x [expr {$x + 1}]

    if {$x > 7} break

    if "$x > 3" continue

    puts "x is $x"

}

 

puts "exited second loop with X equal to $x"

 

执行结果：

x is 1

x is 2

x is 3

x is 4

exited first loop with X equal to 5

 

x is 1

x is 2

x is 3

exited second loop with X equal to 8

 

存在问题：while为什么要用大括号括住 的解释还没有明白。