how to separate the float number from string

Geert_Gruwez, your code doesnt take into account if there is a non numerical character at the end of the string.

no need the Val does this

the aCode will show the location of the problem

maybe Vaalar can evaluate further what he wants to happen ?

In fact it might be better to make sure you never continue past the first number that is found

function TForm1.returnFloat(const s: string): double;
var
   i, startPos, endPos: integer;
begin
   result := 0;

   startPos := 1;
   while ( not ( s[ startPos] in ['0'..'9', DecimalSeparator,ThousandSeparator, '+', '-'])) and
         ( startPos <= length( s)) do
      inc( startPos);

   endPos := startPos;
   while ( s[ endPos] in ['0'..'9', DecimalSeparator,ThousandSeparator, '+', '-']) and
         ( endPos <= length( s)) do
      inc( endPos);

   if endPos >= startPos then
      tryStrToFloat( copy( s, startPos, endPos - startPos), result)
end;

Thx for your help.
I have tested your ideas and it solves  but if i have for example 244e.322 i get 244 afer using Gerts solution. I need to receive 244.322.
The same problem comes out in Mikes solution.

Thx for your help.
I have tested your ideas and it solves some problems  but if i have for example 244e.322 i get 244 afer using Gerts solution. I need to receive 244.322.
The same problem comes out in Mikes solution.

you could first strip all non numerals:

function ConvertFloat(aText: string): Double;
var S: string;
  I, aCode: Integer;
begin
  // First delete all non number characters
  I := 1;
  s := '';
  while (I <= Length(aText)) and (aText[I] in ['-','+',DecimalSeparator,ThousandSeparator,'0'..'9']) do
  begin
    s := s + aText[I];
    Inc(I);
  end;
  // Convert text to float
  Val(S, Result, aCode);
end;

this will never solve all problems
it will get the first number possible

but to resolve this you'll need to specify some rules:

aText := 'abc123.def456-789+1023xxx';

Value to string = '123.456-789+1023';

woops slight mistake

function ConvertFloat(aText: string): Double;
var S: string;
  I, aCode: Integer;
begin
  // First delete all non number characters
  I := 1;
  s := '';
  while (I <= Length(aText)) do
  begin
    if (aText[I] in ['-','+',DecimalSeparator,ThousandSeparator,'0'..'9']) then
      s := s + aText[I];
    Inc(I);
  end;
  // Convert text to float
  Val(S, Result, aCode);
end;

or try StrToFloatDef

Result := StrToFloatDef(S, 0);

Thank you very much Geert,
and thx also to Mike
BR
Vaalar