Shell script help

How can I change my code to be able to compare the size of two files.

if [ -f $1 ] && [ -f $2 ] && [ ! $1 -ef $2 ]; then
    size1=$(du $1)
    size2=$(du $2)
    if [ $1 -gt $2 ]; then
     echo "$1 is bigger"
    else
      echo "$1 is smaller"
    fi
fi

if(sizeof(f1ptr) > sizeof(f2ptr))

i don't think that will work right