nested 循环

Pascal允许在另一个循环中使用一个循环。 以下部分显示了几个例子来说明这个概念。

Pascal中nested for-do loop语句的语法如下 -

for variable1:=initial_value1 to [downto] final_value1 do
begin
   for variable2:=initial_value2 to [downto] final_value2 do
   begin   
      statement(s);
   end;
end;   

Pascal中nested while-do loop语句的语法如下 -

while(condition1)do
begin
   while(condition2) do
   begin
      statement(s);
   end;
   statement(s);
end;

nested repeat ... until loop的语法nested repeat ... until loop Pascal如下 -

repeat
   statement(s);
   repeat
      statement(s);
   until(condition2);
until(condition1);

关于循环嵌套的最后一点是你可以将任何类型的循环放在任何其他类型的循环中。 例如，for循环可以在while循环内，反之亦然。

例子 (Example)

以下程序使用嵌套for循环来查找2到50的素数 -

program nestedPrime;
var
   i, j:integer;
begin
   for i := 2 to 50 do
   begin
      for j := 2 to i do
         if (i mod j)=0  then
            break; {* if factor found, not prime *}
      if(j = i) then
         writeln(i , ' is prime' );
   end;
end.

编译并执行上述代码时，会产生以下结果 -

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