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，但我收到一条警告，提示“变量“i”永远不会被读取，也永远不会被赋值”“for 循环隐式声明循环变量”“声明隐藏了在第 15 行声明的“i””

我该如何解决？

Answer 1

如果我用-gnatl（列出带有错误消息的源代码）编译你的代码，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。循环参数的范围从 loop_parameter_specification 延伸到 loop_statement 的末尾，可见性规则是这样的，循环参数仅在循环的 sequence_of_statements 内可见。

第 6 行的警告告诉您这i（用 ARM 来说是“对象声明”）与第i14 行无关。

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;
}

结果是

$ 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);
      |   ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~