Microsoft qBASIC:

DIM n AS DOUBLE, p AS DOUBLE, k AS INTEGER
CLS
k = 0
p = 1
DO
   INPUT "Vvedite chislo ili 0 dlya kontsa vvoda: ", n
   IF n 0 THEN
      p = p * n
      k = k + 1
   END IF
LOOP UNTIL n = 0
p = EXP(LOG(p) / k)
PRINT "Srednee geometricheskoe = "; p
END

Тестовое решение:
Vvedite chislo ili 0 dlya kontsa vvoda: 3.2
Vvedite chislo ili 0 dlya kontsa vvoda: 11.7
Vvedite chislo ili 0 dlya kontsa vvoda: 8.4
Vvedite chislo ili 0 dlya kontsa vvoda: 0
Srednee geometricheskoe =  6.800461329716477