diff --git a/code.py b/code.py
index 42ffc32..6402cba 100644
--- a/code.py
+++ b/code.py
@@ -1,144 +1,140 @@
-import PySimpleGUI as sg
-import openpyxl
-import xlrd
-import random
-
-def TakeRoll():
-    book = xlrd.open_workbook('sample.xlsx')
-    sheet = book.sheet_by_index(0)
-    book = openpyxl.load_workbook(filename='sample.xlsx')
-    ins_sheet = book.active
-    if sheet.ncols == 2:
-        ins_sheet['C1'] = 'Scredit'
-        idx = random.randint(2, sheet.nrows)
-        stu = str(ins_sheet.cell(row=idx, column=1).value) + ins_sheet.cell(row=idx, column=2).value
-        i = 2
-        while i <= sheet.nrows:
-            ins_sheet.cell(row=i, column=3).value = 0
-            i += 1
-        book.save(filename='sample.xlsx')
-    else:
-        max = 0
-        credit = ins_sheet['C']
-        i = 1
-        while i <= sheet.nrows-1:
-            credit[i].value *= 2
-            i += 1
-        i = 1
-        while i <= sheet.nrows-1:
-            if credit[i].value > max:
-                max = credit[i].value
-            i += 1
-        '''                
-        while i<=sheet.nrows:
-            if ins_sheet.cell(row=i, column=3).value > max:
-                max = ins_sheet.cell(row=i, column=3).value
-            i += 1
-        '''
-        max += 1
-        slct = []
-        i = 1
-        while i <= sheet.nrows-1:
-            credit[i].value = max - credit[i].value
-            r = 1
-            while r <= int(credit[i].value):
-                slct.append(i)
-                r += 1
-            i += 1
-        idx = random.randint(0, len(slct)-1)
-        stu = str(ins_sheet.cell(row=slct[idx]+1, column=1).value) + ins_sheet.cell(row=slct[idx]+1, column=2).value
-    return stu, slct[idx]+1
-
-def CreditUpdate(stu, isInc, point):
-    book = openpyxl.load_workbook(filename='sample.xlsx')
-    sheet = book.active
-    if isInc == True:
-        sheet.cell(row=stu, column=3).value += point
-    else:
-        sheet.cell(row=stu, column=3).value -= point
-    book.save(filename='sample.xlsx')
-
-layoutA = [
-    [sg.Text('被点到的同学：'), sg.Text('', key = 'roll')],
-    [sg.Button('点名')]
-]
-
-layoutB1 = [
-    [sg.Button('是'), sg.Button('否')],
-]
-
-layoutB2 = [
-    [sg.Button('是'), sg.Button('否')],
-]
-
-layoutB3 = [
-    [sg.Button('是'), sg.Button('否')],
-]
-
-layoutC = [
-    [sg.Button('回答问题'), sg.Button('请ta坐下')],
-]
-
-List = [0.5, 1.0, 1.5, 2.0, 2.5, 3.0]
-layoutD = [
-    [sg.Drop(List,
-            default_value = None,
-            size = (30, 6),
-            enable_events = True,
-            key = 'point'
-            )],
-    [sg.Button('确认')]
-]
-
-window = sg.Window('点名', layoutA)
-while True:
-    event, values = window.read()
-    if event == sg.WINDOW_CLOSED:
-        break
-    if event == '点名':
-        ret, rownum = TakeRoll()
-        window['roll'].update(value=ret)
-        window = sg.Window('该同学是否到位？', layoutB1)
-        while True:
-            event, values = window.read()
-            if event in (sg.WINDOW_CLOSED, '否'):
-                break
-            if event == '是':
-                CreditUpdate(rownum, True, 1.0)
-                window = sg.Window('接下来...', layoutC)
-                while True:
-                    event, values = window.read()
-                    if event in (sg.WINDOW_CLOSED, '请ta坐下'):
-                        break
-                    if event == '回答问题':
-                        window = sg.Window('该同学能否复述问题？', layoutB2)
-                        while True:
-                            event, values = window.read()
-                            if event == sg.WINDOW_CLOSED:
-                                break
-                            if event == '是':
-                                CreditUpdate(rownum, True, 0.5)
-                                window = sg.Window('该同学答对问题了吗？', layoutB3)
-                                while True:
-                                    event, values = window.read()
-                                    if event in (sg.WINDOW_CLOSED, '否'):
-                                        break
-                                    if event == '是':
-                                        window = sg.Window('给ta打分：', layoutD)
-                                        while True:
-                                            event, values = window.read()
-                                            if event == sg.WINDOW_CLOSED:
-                                                break
-                                            if event == '确认':
-                                                CreditUpdate(rownum, True, values['point'])
-                                                break
-                                        break
-                                break
-                            if event == '否':
-                                CreditUpdate(rownum, False, 1.0)
-                                break
-                        break
-                break
-        break
-
-window.close()
\ No newline at end of file
+import PySimpleGUI as sg
+import openpyxl
+import xlrd
+import random
+
+def TakeRoll():
+    book = xlrd.open_workbook('sample.xlsx')
+    sheet = book.sheet_by_index(0)
+    book = openpyxl.load_workbook(filename='sample.xlsx')
+    ins_sheet = book.active
+    if sheet.ncols == 2:
+        ins_sheet['C1'] = 'Scredit'
+        idx = random.randint(2, sheet.nrows)
+        stu = str(ins_sheet.cell(row=idx, column=1).value) + ins_sheet.cell(row=idx, column=2).value
+        i = 2
+        while i <= sheet.nrows:
+            ins_sheet.cell(row=i, column=3).value = 0
+            i += 1
+        book.save(filename='sample.xlsx')
+        return stu, idx
+    else: #学生表中含有已创建的SCredit列
+        max = 0
+        credit = ins_sheet['C'] #将SCredit列存入redit数组
+        i = 1
+        while i <= sheet.nrows-1:
+            credit[i].value *= 2 #将所有积分值整数化（所有非整数积分值小数部分均为0.5）
+            i += 1
+        i = 1
+        while i <= sheet.nrows-1:
+            if credit[i].value > max:
+                max = credit[i].value
+            i += 1
+        max += 1 #求出最大积分值并加1
+        slct = []
+        i = 1
+        while i <= sheet.nrows-1:
+            credit[i].value = max - credit[i].value #倒转积分值，将最大的积分值置为1，其余积分依次增大
+            r = 1
+            while r <= int(credit[i].value):
+                slct.append(i)
+                r += 1 #第i个学生倒转后的积分值即为slct数组中对应第i个学生的元素个数，和该生被选中的概率呈负相关
+            i += 1
+        idx = random.randint(0, len(slct)-1)
+        stu = str(ins_sheet.cell(row=slct[idx]+1, column=1).value) + ins_sheet.cell(row=slct[idx]+1, column=2).value
+        return stu, slct[idx]+1
+
+def CreditUpdate(stu, isInc, point):
+    book = openpyxl.load_workbook(filename='sample.xlsx')
+    sheet = book.active
+    if isInc == True:
+        sheet.cell(row=stu, column=3).value += point
+    else:
+        sheet.cell(row=stu, column=3).value -= point
+    book.save(filename='sample.xlsx')
+
+layoutA = [
+    [sg.Text('被点到的同学：'), sg.Text('', key = 'roll')],
+    [sg.Button('点名')]
+]
+
+layoutB1 = [
+    [sg.Button('是'), sg.Button('否')],
+]
+
+layoutB2 = [
+    [sg.Button('是'), sg.Button('否')],
+]
+
+layoutB3 = [
+    [sg.Button('是'), sg.Button('否')],
+]
+
+layoutC = [
+    [sg.Button('回答问题'), sg.Button('请ta坐下')],
+]
+
+List = [0.5, 1.0, 1.5, 2.0, 2.5, 3.0]
+layoutD = [
+    [sg.Drop(List,
+            default_value = None,
+            size = (30, 6),
+            enable_events = True,
+            key = 'point'
+            )],
+    [sg.Button('确认')]
+]
+
+window = sg.Window('点名', layoutA)
+while True:
+    event, values = window.read()
+    if event == sg.WINDOW_CLOSED:
+        break
+    if event == '点名':
+        ret, rownum = TakeRoll()
+        window['roll'].update(value=ret)
+        window = sg.Window('该同学是否到位？', layoutB1)
+        while True:
+            event, values = window.read()
+            if event in (sg.WINDOW_CLOSED, '否'):
+                break
+            if event == '是':
+                CreditUpdate(rownum, True, 1.0)
+                window = sg.Window('接下来...', layoutC)
+                while True:
+                    event, values = window.read()
+                    if event in (sg.WINDOW_CLOSED, '请ta坐下'):
+                        break
+                    if event == '回答问题':
+                        window = sg.Window('该同学能否复述问题？', layoutB2)
+                        while True:
+                            event, values = window.read()
+                            if event == sg.WINDOW_CLOSED:
+                                break
+                            if event == '是':
+                                CreditUpdate(rownum, True, 0.5)
+                                window = sg.Window('该同学答对问题了吗？', layoutB3)
+                                while True:
+                                    event, values = window.read()
+                                    if event in (sg.WINDOW_CLOSED, '否'):
+                                        break
+                                    if event == '是':
+                                        window = sg.Window('给ta打分：', layoutD)
+                                        while True:
+                                            event, values = window.read()
+                                            if event == sg.WINDOW_CLOSED:
+                                                break
+                                            if event == '确认':
+                                                CreditUpdate(rownum, True, values['point'])
+                                                break
+                                        break
+                                break
+                            if event == '否':
+                                CreditUpdate(rownum, False, 1.0)
+                                break
+                        break
+                break
+        break
+
+window.close()
+