Ada编译警告

Question

with Ada.Text_IO, Ada.Integer_Text_IO;
use  Ada.Text_IO, Ada.Integer_Text_IO;

procedure factorial_ada is

    n, i : Integer;
    output : Integer := 1;

begin
    Put_Line("Enter the number to be taken factorial of: ");
    Get(n);

   -- Begin Loop
    for i in 2..n
    loop
        output := output * i;
    end loop;

    Put("Factorial of "); 
    Put(n); 
    Put(" is "); 
    Put(output);

end factorial_ada;  

我的代码可以编译并运行，但是我得到了一个警告，它说“变量"i”永远不会被读取和赋值“"for loop隐式声明循环变量”“声明隐藏了在第15行声明的"i”“

我该如何解决这个问题？

Answer 1

如果我用-gnatl编译您的代码(源代码清单，行中有错误消息)，它会给出

 1. with Ada.Text_IO, Ada.Integer_Text_IO;
 2. use  Ada.Text_IO, Ada.Integer_Text_IO;
 3.
 4. procedure factorial_ada is
 5.
 6.     n, i : Integer;
           |
    >>> warning: variable "i" is never read and never assigned

 7.     output : Integer := 1;
 8.
 9. begin
10.     Put_Line("Enter the number to be taken factorial of: ");
11.     Get(n);
12.
13.    -- Begin Loop
14.     for i in 2..n
            |
    >>> warning: for loop implicitly declares loop variable
    >>> warning: declaration hides "i" declared at line 6

15.     loop
16.         output := output * i;
17.     end loop;
18.
19.     Put("Factorial of ");
20.     Put(n);
21.     Put(" is ");
22.     Put(output);
23.
24. end factorial_ada;

第14行的警告提醒您(ARM 5.5(11))

不应为循环参数提供object_declaration，因为循环参数是由loop_parameter_specification自动声明的。循环参数的作用域从loop_parameter_specification延伸到loop_statement的末尾，可见性规则使得循环参数仅在循环的sequence_of_statements中可见。

第6行的警告告诉您，此i (ARM语言中的“对象声明”)与第14行的i无关。

这类似于C++规则:编写

#include <stdio.h>
int main() {
  int i;
  int output = 1;
  int n = 12;
  for (int i = 2; i <= n; i++) {
    output *= i;
  }
  printf("factorial %d is %d\n", i, output);
  return 0;
}

结果：

$ g++ hk.cc -Wall
hk.cc: In function 'int main()':
hk.cc:9:9: warning: 'i' is used uninitialized in this function [-Wuninitialized]
    9 |   printf("factorial %d is %d\n", i, output);
      |   ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~