Congrats on getting a handle on the switch statement and menu handling. So what calculations are wrong?

if ( crdt == 0 ) {
                        blnce = strt_blnce + dpst;
                  } else if (crdt > 0) {
                   blnce3 = blnce2 + dpst;
blnce3 and blnce2 are not initialized.
Its best that you just initialize everything the way you want it before showing the menu and starting the loop.

if (withdrw > blnce) {
                     printf("Please enter a smaller amt. \n");
                     printf("How much do you want to withdraw?  ");
                     scanf("%f", &withdrw);
                     blnce2 = blnce - withdrw;
                     blnce = blnce2;
Put that in a loop for 2 reasons.
1.) The user can keep entering more than their balance, so they need to be told that every time.
2.) Right now, if they enter more than their balance, the next value they enter is not used by you at all...just goes on.

Make sure in the loop they can exit if they want, and maybe show them how much is actually available.

Thats it for now...back to work for me