#!/bin/bash

if [ -z $1 ]; then
    for file in ./*; do
        [ -f "${file}" ] && ((files++))
    done
    echo "Number of files in directory: ${files-0}"

else
    for file in *.$1; do
        [ -f "${file}" ] && ((files++))
    done
    echo "Number of files with extension $1: ${files-0}"
fi