TCL允许使用一个循环内的另一个循环。下面的内容展示几个例子来说明这个概念。
Tcl语言的嵌套的循环语句的语法如下：
for {initialization} {condition} {increment} {
for {initialization} {condition} {increment} {
statement(s);
}
statement(s);
}
Tcl语言嵌套while循环语句的语法如下：
while {condition} {
while {condition} {
statement(s);
}
statement(s);
}
在循环嵌套最后需要说明的是，可以把任何类型循环嵌套在其他类型循环内。例如，for循环可以是一个while循环的内循环，或反之亦然。
下面的程序使用嵌套for循环从2至100找出所有的素数：
#!/usr/bin/tclsh
set j 0;
for {set i 2} {$i<100} {incr i} {
for {set j 2} {$j <= [expr $i/$j] } {incr j} {
if { [expr $i%$j] == 0 } {
break
}
}
if {$j >[expr $i/$j] } {
puts "$i is prime"
}
}
当上述代码被编译和执行时，它产生了以下结果：
2 is prime 3 is prime 5 is prime 7 is prime 11 is prime 13 is prime 17 is prime 19 is prime 23 is prime 29 is prime 31 is prime 37 is prime 41 is prime 43 is prime 47 is prime 53 is prime 59 is prime 61 is prime 67 is prime 71 is prime 73 is prime 79 is prime 83 is prime 89 is prime 97 is prime
