100 ! The graph of the logarithmic function with base a
110 DEF f(x)=LOG10(x)/LOG10(a)
120 INPUT a
130 SET WINDOW 0,10,-5,5
140 DRAW GRID 
150 SET POINT STYLE 1
160 FOR x=0.01 TO 10 STEP 0.01 
170    PLOT POINTS: x,f(x)
180 NEXT x
190 END
 