Here's a xassoccnt version of sharing/coupling counters that does not require more setup than defining a group of coupled counters, here figure and lstlisting. (This requires xassoccnt v0.6)
After that, the figure / listings counter step together.
\documentclass{book}
\usepackage[T1]{fontenc}
\usepackage{textgreek}
\usepackage[utf8]{inputenc}
\usepackage[greek,english]{babel}
\usepackage{listings}
\usepackage{xassoccnt}
\DeclareCoupledCounters[name=figurelistingsgroup]{figure,lstlisting}
\renewcommand{\lstlistingname}{Εικόνα}
\addto\captionsgreek{\renewcommand{\figurename}{Εικόνα}}
\begin{document}
\chapter{First}
\begin{figure}[ht]
\caption{This is a figure.}
\end{figure}
\begin{lstlisting}[language=C,caption={Hello World},floatplacement={ht}]
#include<stdio.h>
int main(int argc,char **argv)
{
printf("Hello World!\n");
return(0);
}
\end{lstlisting}
\begin{figure}[ht]
\caption{A dummy figure}
\end{figure}
\begin{figure}[ht]
\caption{Yet another dummy figure}
\end{figure}
\begin{lstlisting}[caption={Hello World again},language=C,floatplacement={ht}]
#include<stdio.h>
int main(int argc,char **argv)
{
printf("Hello World!\n");
return(0);
}
\end{lstlisting}
\end{document}

placeholder. – vaiski Apr 02 '16 at 12:18\usepackage[demo]{graphicx}to prevent such non-compilable examples – Apr 02 '16 at 12:30demomode? ;-) – Apr 02 '16 at 13:30