#define VCmsg "Installing Microsoft Visual C++ Redistributable...."

[Run]
; 2015
Filename: "{app}\vc_redist.x64.exe"; StatusMsg: "{#VCmsg}"; Check: IsWin64 and not VCinstalled2015
Filename: "{app}\vc_redist.x86.exe"; StatusMsg: "{#VCmsg}"; Check: not IsWin64 and not VCinstalled2015
; other versions


[Code]
function VCinstalled: Boolean;
// Works for every version of Visual C++ Redistributable except 2015
 var
  names: TArrayOfString;
  i: Integer;
  dName, key, year: String;
 begin
  // Year of redistributable to find; leave null to find installation for any year.
  year := '2017';
  Result := False;
  key := 'Software\Microsoft\Windows\CurrentVersion\Uninstall';
  // Get an array of all of the uninstall subkey names.
  if RegGetSubkeyNames(HKEY_LOCAL_MACHINE, key, names) then
   // Uninstall subkey names were found.
   begin
    i := 0
    while ((i < GetArrayLength(names)) and (Result = False)) do
     // The loop will end as soon as one instance of a Visual C++ redistributable is found.
     begin
      // For each uninstall subkey, look for a DisplayName value.
      // If not found, then the subkey name will be used instead.
      if not RegQueryStringValue(HKEY_LOCAL_MACHINE, key + '\' + names[i], 'DisplayName', dName) then
       dName := names[i];
      // See if the value contains both of the strings below.
      Result := (Pos(Trim('Visual C++ ' + year),dName) * Pos('Redistributable',dName) <> 0)
      i := i + 1;
     end;
   end;
 end;

 [Code]
function VCinstalled2015: Boolean;
// Works only for Visual C++ Redistributable 2015, because the label is
// Microsoft Visual C++ 2015 x64 Minimum Runtime - 14.0.23026
 var
  names: TArrayOfString;
  i: Integer;
  dName, key, year: String;
 begin
  // Year of redistributable to find; leave null to find installation for any year.
  year := '2015';
  Result := False;
  key := 'Software\Microsoft\Windows\CurrentVersion\Uninstall';
  // Get an array of all of the uninstall subkey names.
  if RegGetSubkeyNames(HKEY_LOCAL_MACHINE, key, names) then
   // Uninstall subkey names were found.
   begin
    i := 0
    while ((i < GetArrayLength(names)) and (Result = False)) do
     // The loop will end as soon as one instance of a Visual C++ redistributable is found.
     begin
      // For each uninstall subkey, look for a DisplayName value.
      // If not found, then the subkey name will be used instead.
      if not RegQueryStringValue(HKEY_LOCAL_MACHINE, key + '\' + names[i], 'DisplayName', dName) then
       dName := names[i];
      // See if the value contains both of the strings below.
      Result := (Pos(Trim('Visual C++ ' + year),dName) <> 0)
      i := i + 1;
     end;
   end;
 end;