Question

我一直在尝试运行以下程序，但编译器一直告诉我标识符n不起作用。程序应该做的是执行n的值，即过程文件的次数。 n不能是常量，因为在运行时读取。有人可以帮帮我吗？

Program num;

Var
f:Text;
b,g:array [1..n] of integer;
m,n:Integer;
c:String[1];

Procedure thenum (a:array [1..n] of integer);
Begin
for i:= 1 to n do
repeat
Read (f,a[i]);
Write(a[i]);
Until(a[i]=' ');
End;
End;

Procedure sth ( j:array [1..n] of integer);
begin
for k:= 1 to n do
while not seekEoln and eof(f) do
begin
read(f,j[k]);
Write(j[k]);
end;
End;
End;

procedure space;
begin

Read(f,c);
Write(c);
end;

procedure file
begin
Assign(f,'textfile.txt');
Reset(f);
thenum (b[a]);
space;
sth (g[k]);
Close(f);
Readln;
End;


Begin
Assign(f,'textfile.txt');
Reset(f);
repeat
Read (f,n);
Write(n);
Until(n=' ');
End;
Read(f,c);
Write(c);
while not seekEoln and eof(f) do
begin
read(f,m);
Write(m);
end;
file;
End.

Answer 1

编译器在编译时不知道n的值。通常，您可以将一些适当的最大大小定义为常量，例如N_MAX，然后将其用于您的数组维度。在运行时，您将确保n <= N_MAX。

Answer 2

Pascal不支持声明为固定长度的可变大小的数组。

大多数现代编译器（Delphi / FreePascal）都支持动态数组，其中长度是在运行时设置的。下限始终为零，上限为length - 1：

var
  Arr: array of Integer;
  L, H, Len: Integer;
  ArraySize: Integer;
begin
  Len := 10;                // Value of Len can be input at runtime
  SetLength(Arr, Len);
  L := Low(Arr);            // Will be 0
  H := High(Arr);           // Will be Len - 1, because first index is 0
  ArrSize := Length(Arr);   // Will be Len
  WriteLn('Low: ', L, ' High: ', H, ' Length: ', ArrSize);  
  ReadLn;
end;

这是一个完整的示例（在Delphi中，但它应该与FreePascal一起使用）接受来自控制台的输入并使用它来设置长度，并显示如上所述的低，高和长度值。它还演示了如何将数组传递给不了解数组中元素数量的过程。

program Project1;

uses
  SysUtils;

// Lists the items in an array to the console without
// knowing in advance the size of the array
procedure ListAnArray(const TheArray: array of Integer);
var
  x: Integer;
begin
  // Retrieve the valid low and high indexes, and
  // loop through the array to output each value
  for x := Low(TheArray) to High(TheArray) do
    WriteLn('TheArray ', x, ' value: ', TheArray[x]);
end;

// The variables we'll be using (a few more than I would 
// normally use, just to make the example clearer)
var
  ArraySize: Integer;            // Length of array input by user
  lowIdx, highIdx: Integer;      // low array index, high index
  ArrayLen: Integer;             // Length of array (set at runtime)
  Counter: Integer;              // Loop counter
  TestArray: array of Integer;   // Our dynamic array

begin
  Write('Enter array length: ');      // Prompt user
  Readln(ArraySize);                  // Read input

  Writeln('You entered: ', ArraySize);
  WriteLn('');                        // Blank line separator

  SetLength(TestArray, ArraySize);    // Size the array
  lowIdx := Low(TestArray);           // Get low index (always 0)
  highIdx := High(TestArray);         // # of elements - 1
  ArrayLen := Length(TestArray);      // Same as user entered
  Writeln('Low: ', lowIdx,            // Output what we've learned
          ' High: ', highIdx,
          ' Length: ', ArrayLen);
  WriteLn('');                        // Blank line separator

  for Counter := lowIdx to highIdx do // Fill the array with values
    TestArray[Counter] := Counter * Counter;

  ListAnArray(TestArray);             // Pass array to procedure
  WriteLn('');                        // Blank line separator

  WriteLn('Press Enter to quit...');  // Pause to allow reading.
  Readln;
end.

为什么编译器不能接受类似[1..n]的数组？

2 个答案: