#!/bin/bash
i=0
thedate="2018-03-28"
enddate="2018-04-02"
while [ "$thedate" != "$enddate" ]; do
    thedate=$( date -d "$thedate + $i days" +%F )

    new_date=$( date -d "$thedate " +%Y%m%d )
    printf 'The date is "%s"n' "$new_date"
    i=$(( i + 1 ))
done

The date is "20180328"
The date is "20180329"
The date is "20180330"
The date is "20180331"
The date is "20180401"
The date is "20180402"