gpp: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/gpp - from package: gpp

You may install the required package with command apt-get install {package}

Error in other languages:
gpp: bevel nie gevind nie
gpp: comandă negăsită
gpp: comando não encontrado
gpp: commande introuvable
gpp: command not found
gpp: käsku ei ole
gpp: không tìm thấy lệnh
gpp: komanda nerasta
gpp: Kommando nicht gefunden.
gpp: kommandot finns inte
gpp: komut yok
gpp: nie znaleziono polecenia
gpp: níor aimsíodh an t-ordú
gpp: no se encontró la orden
gpp: no s'ha trobat l'ordre
gpp: opdracht niet gevonden
gpp: parancs nem található
gpp: perintah tidak ditemukan
gpp: príkaz nenájdený
gpp: příkaz nenalezen
gpp: команда не найдена
gpp: командата не е открита
gpp: 命令找不到
gpp: コマンドが見つかりません