Bash determine whether parameter variables ($1, $2, $3, etc.) have been set

Many of the posts I just read have many answers that cover this, but I don't understand what I'm doing really; it's been hit & miss.

The .sh script I'm working with:

#!/bin/bash  
# init  

input=$1  
output=$(ping -c 1 "$input" 2>/dev/null)                
if [ $? -eq 0 ]; then                  
   ip=$(printf '%s' "$output" | gawk -F'[()]' '/PING/{print $2}'  2>/dev/null)     
   echo "$ip";                
   sleep 2              
else         
   echo "Host not found";      
fi         

Many of the posts I have just read cover this, and state there are several different methods that can be used to accomplish this, but I still don't really understand how to go about using them properly. Basically, I'm trying to check if the variable "$1" has been set by an argument, and display something like:

echo No argument given  

if the variable is empty, instead of just pinging no host. My question is: How should I go about doing this without over-complicating things?

Help is always appreciated, thanks in advance.

PS: I'm still fairly new to linux environment, so go easy on me.

I'd add a check at the begining. In case of failure display a message and exit.

#!/bin/bash  
# init  

if [ -z "$1" ]; then
  echo No argument given 
  exit
fi

input=$1  
output=$(ping -c 1 "$input" 2>/dev/null)                
if [ $? -eq 0 ]; then                  
   ip=$(printf '%s' "$output" | gawk -F'[()]' '/PING/{print $2}'  2>/dev/null)     
   echo "$ip";                
   sleep 2              
else         
   echo "Host not found";      
fi        

If you want to know the number of args passed, use $#. Like this:

if [ $# -eq 0 ]; then
  echo "No argument given"
fi

Hope that helps.