PROGRAM USRDEF
C
C This program motivates the utility of user-defined functions
C
      IMPLICIT NONE
      REAL X, Y, Z
      
      PRINT *, 'Please enter a real number'
      READ *, X
      PRINT *, 'The base two logarithm is ', LOG10(X)/LOG10(2.0)

      PRINT *, 'Please enter another real number'
      READ *, Y
      PRINT *, 'The base two logarithm is ', LOG10(Y)/LOG10(2.0)

      PRINT *, 'Please enter a third real number'
      READ *, Z
      PRINT *, 'The base two logarithm is ', LOG10(Z)/LOG10(2.0)

      STOP
      END