自己写了一个四舍五入的函数 但运行时出现invalied pointer operation问题 忘高手帮我解决

Question

代码function sswr(ss:string;j:integer):string;//j代表想要保留的小数点后的位数，SS是传进来的值
var
    arr:array of pchar;
    k,i,cd:integer;
begin
  result:='';
  cd:=length(ss);
  setlength(arr,cd);
  for i:=1 to cd do begin
    arr[i]:=pchar(copy(ss,i,1));
    case j of
      1: begin
           if arr[i]='.' then  begin
              if cd-i<2 then  begin
                result:=ss;
                break;
              end else begin
                k:=i;
                k:=k+2;
                arr[k]:=pchar(copy(ss,k,1));
                 if  arr[k]<='4' then begin
                    result:=copy(ss,1,k-1);
                    break;
                 end else begin
                    arr[k-1]:=arr[k-1]+1;
                    result:=copy(ss,1,k-2)+arr[k-1];
                    break;
                 end;
              end;
           end;
           if i=cd then
             begin
             result:=ss+'.0';
             break;
             end;
         end;
      2: begin
           if arr[i]='.' then  begin
              if cd-i<3 then begin
                case (cd-i)  of
                  1: begin
                       result:=ss+'0';
                       break;
                     end;
                  2:begin
                     result:=ss;
                     break;
                    end;
                 end;
              end else begin
                k:=i;
                k:=k+3;
                arr[k]:=pchar(copy(ss,k,1));
                 if  arr[k]<='4' then begin
                    result:=copy(ss,1,k-1);
                    break;
                 end else begin
                    arr[k-1]:=arr[k-1]+1;
                    result:=copy(ss,1,k-2)+arr[k-1];
                    break;
                 end;
              end;
           end;
           if i=cd then
               begin
               result:=ss+'.0';
               break;
               end;
         end;
      3: begin
           if arr[i]='.' then  begin
              if cd-i<4 then  begin
                case (cd-i) of
                1: begin
                     result:=ss+'00';
                     break;
                   end;
                2: begin
                     result:=ss+'0';
                     break;
                   end;
                3:begin
                    result:=ss;
                    break;
                  end; end;
              end else begin
                k:=i;
                k:=k+4;
                arr[k]:=pchar(copy(ss,k,1));
                 if  arr[k]<='4' then begin
                    result:=copy(ss,1,k-1);
                    break;
                 end else begin
                    arr[k-1]:=arr[k-1]+1;
                    result:=copy(ss,1,k-2)+arr[k-1];
                    break;
                 end;
              end;
           end;
           if i=cd then
             begin
             result:=ss+'.000';
             break;
             end;         end;
      4: begin
           if arr[i]='.' then  begin
              if cd-i<5 then  begin
                case (cd-i) of
                1: begin
                     result:=ss+'000';
                      break;
                   end;
                2: begin
                     result:=ss+'00';
                      break;
                   end;
                3: begin
                     result:=ss+'0';
                      break;
                   end;
                4:begin
                    result:=ss;
                    break;
                  end; end;
              end else begin
                k:=i;
                k:=k+5;
                arr[k]:=pchar(copy(ss,k,1));
                 if  arr[k]<='4' then begin
                    result:=copy(ss,1,k-1);
                    break;
                 end else begin
                    arr[k-1]:=arr[k-1]+1;
                    result:=copy(ss,1,k-2)+arr[k-1];
                    break;
                 end;
              end;
           end;
           if i=cd then
             begin
             result:=ss+'.0000';
             break;
             end;
         end;
       5: begin
             if arr[i]='.' then  begin
                if cd-i<6 then  begin
                  case (cd-i) of
                  1: begin
                       result:=ss+'0000';
                       break;
                     end;
                   2: begin
                       result:=ss+'000';
                       break;
                     end;
                   3: begin
                       result:=ss+'00';
                       break;
                     end;
                   4: begin
                       result:=ss+'0';
                       break;
                     end;
                   5:begin
                       result:=ss;
                       break;
                     end; end;
                end else begin
                  k:=i;
                  k:=k+6;
                  arr[k]:=pchar(copy(ss,k,1));
                   if  arr[k]<='4' then begin
                      result:=copy(ss,1,k-1);
                      break;
                   end else begin
                      arr[k-1]:=arr[k-1]+1;
                      result:=copy(ss,1,k-2)+arr[k-1];
                      break;
                   end;
                end;
             end;
             if i=cd then
               begin
               result:=ss+'.00000';
               break;
               end;
          end;
  end;
end;
end;

Answer 1

不看了，来个简单defunction myRound(x:extended;n :integer) : extended;  //x浮点数，n整数保留的位数，返回还是浮点
begin
  x := x * exp(n*ln(10));
  if (int(x) * 10 + 5) > int(x * 10) then
  begin
    result := floor(x);
  end else
  begin
    result := ceil(x);
  end;
  result := result /exp(n*ln(10));
end;调用
var
y :extended;
begin 
y := myRound(3.1415926,4);
end;

Answer 2

最简单的：FloatToStrF(Value,ffFixed,18,j) :string;

Answer 3

直接使用RoundTo函数，需要uses中加入math。
RoundTo(1.245, -2);  = 1.25需要注意的是，旧的Delphi版本Round函数采用的是四舍六入，逢五的时候是前面是奇数才入，是偶数则不入，delphi手册帮助中的示例如下：
RoundTo(1234567, 3) 1234000
RoundTo(1.234, -2) 1.23
RoundTo(1.235, -2) 1.24
RoundTo(1.245, -2) 1.24但delphi 7已经不是这样的了，是直接四舍五入的：RoundTo(1.245, -2) = 1.25。