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

>>12
intENTERPRISE_C(char *f1, char *f2){
    if(strlen(f1) > strlen(f2) goto file1;
    printf("File 2 is bigger\n");
    goto end;
   file1:
    printf("File 1 is bigger\n");
   end:
    return 0;
}