How to replace string in delphi

To replace string in delphi, we can use 'StringReplace' function. The pattern is

function StringReplace ( const SourceString, 
OldPattern, NewPattern : string; 
Flags : TReplaceFlags ) : string;

It replaces the first or all occurences of a substring 'OldPattern' in 'SourceString' with 'NewPattern' according to 'Flags' settings.
There are two Flags can be applied. It may be none, one, or both of these values:

rfReplaceAll  : Change all occurrences
rfIgnoreCase  : Ignore case when searching

Below is the example code:

var
  before, after : string;
begin
  // Try to replace all occurrences of a or A to THE
  before := 'It is a kind of fruit';
  after  := StringReplace(before, ' a ', ' THE ',
                          [rfReplaceAll, rfIgnoreCase]);
  ShowMessage('Before = '+before);
  ShowMessage('After  = '+after);
end;

It will output this alert

Before = It is a kind of fruit
After  = It is THE kind of fruit