If (x(0) >= 0) And (y(0) >= 0) If f(i) >= 0 Then For j = x(i) To x(i) + 1 Step 0.0001 PSet (j,y(i)

If ...Then ...
你的If语句里面没有ThenIf (x(0) >= 0) And (y(0) >= 0) And (xa >= 0) And (ya >= 0) ThenIf f(i) >= 0 ThenFor j = x(i) To x(i) + 1 Step 0. 0001PSet (j, y(i))Next jx(i + 1) = x(i) + 1y(i + 1) = y(i)f(i + 1) = f(i) - yaElseFor j = y(i) To y(i) + 1 Step 0. 0001PSet (x(i), j)Next jy(i + 1) = y(i) + 1x(i + 1) = x(i)f(i + 1) = f(i) + xaEnd If这个那里缺少结束语句啊最后还缺少一个 End If