protoc-c: 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 CentOS possible default full paths are:

/usr/bin/protoc-c - from package: protobuf-c

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/protoc-c - from package: protobuf-c-compiler

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

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