实现一个计算器功能需要使用栈。
比如我要计算：7-3*2+1，这个得先乘除后加减，这就需要栈了。
1.自左向右扫描表达式，凡是遇到操作数一律进操作数栈。
2.当遇到运算符时，如果他的优先级比运算符栈栈顶元素的优先级高就栈。反之，取出栈顶运算符和操作数栈顶的两个连续操作数运算，并将结果存入操作数栈，然后继续比较该运算符与栈顶的运算符的优先级。
3.左括号一律进运算符栈，右括号一律不进运算符栈，取出栈顶运算符和操作数栈顶的两个连续操作数运算，并将结果存入操作数栈，直到取出左括号为止。
然而，在Python中由于有eval函数的存在，就不需要使用栈来实现计算器了。
eval(expression, globals=None, locals=None) --- 官方文档中的解释是，将字符串str当成有效的表达式来求值并返回计算结果。
例如：
接下来是利用tkinter编写的代码：
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from tkinter import * from tkinter import messagebox from math import * root = Tk() root.geometry('430x300+400+100') root.title('计算器') # 总显示 frame = Frame() Main = Listbox(frame, height=5, width=50) scb = Scrollbar(frame) scb.pack(side=RIGHT) Main.pack() scb.pack() Main['yscrollcommand'] = scb.set scb['command'] = Main.yview # 记录输入字符串 record = '' # 结果字符串 result = '' # 优先级 priotry = {} priotry['+'] = 0 priotry['-'] = 0 priotry['*'] = 1 priotry['/'] = 1 priotry['%'] = 1 priotry['^'] = 2 # 定义各按钮符号 def appendstr(temp): global record if len(record) != 0: record = record + temp else: record = record + temp if Main.get(0) != '': alltemp = Main.get(0) alltemp = alltemp + temp Main.delete(0) Main.insert(0, alltemp) else: Main.insert(0, temp) # 初始化数字按钮 b = [None] * 10 for i in range(0, 10): b[i] = Button(text=str(i), width=10) # b[i]=Button(text=str(i),width=10,command=lambda:appendstr(str(i)))错误，因为i在后面又被重新使用 b[0]['command'] = lambda: appendstr('0') b[1]['command'] = lambda: appendstr('1') b[2]['command'] = lambda: appendstr('2') b[3]['command'] = lambda: appendstr('3') b[4]['command'] = lambda: appendstr('4') b[5]['command'] = lambda: appendstr('5') b[6]['command'] = lambda: appendstr('6') b[7]['command'] = lambda: appendstr('7') b[8]['command'] = lambda: appendstr('8') b[9]['command'] = lambda: appendstr('9') # 布局数字按钮 for i in range(7, 10): b[i].grid(row=1, column=i - 7) for i in range(4, 7): b[i].grid(row=2, column=i - 4) for i in range(1, 4): b[i].grid(row=3, column=i - 1) b[0].grid(row=4, column=0) def cal(temp): global record global result record = record + '#' alltemp = Main.get(0) Main.delete(0) if temp == '=': result = eval(alltemp) elif temp == '1/x': if result == '0': messagebox.showerror('计算错误', '0没有倒数') else: print(alltemp) result = str(1 / float(alltemp)) elif temp == 'sin': result = str(sin(float(alltemp))) elif temp == 'cos': result = str(cos(float(alltemp))) elif temp == 'tan': result = str(tan(float(alltemp))) alltemp = alltemp + '=' + str(result) Main.insert(0, alltemp) Main.insert(0, '') f = open("我的计算日志.txt", "a+") # 以追加的方式 f.write('\n' + str(alltemp)) # 写完通过\n进行换行 # 清除一个字符 def delete(): global record global Main # 防止多次点击清除上一行 if record == '': return index = record.rfind(' ') record = record[0:index] Main.delete(0) if index - 1 >= 0: # 如果是第一字符就不插入空白行 Main.insert(0, record) # 清楚一行 def deleteall(): global record global Main record = '' Main.delete(0) Main.insert(0, '') # 初始化符号按钮 bdel = Button(text='C', command=delete, width=5) bdelall = Button(text='AC', command=deleteall, width=5) bsub = Button(text='-', width=2, command=lambda: appendstr('-')) badd = Button(text='+', width=2, command=lambda: appendstr('+')) bmul = Button(text='*', width=2, command=lambda: appendstr('*')) bdiv = Button(text='/', width=2, command=lambda: appendstr('/')) bmod = Button(text='%', width=2, command=lambda: appendstr('%')) bcon = Button(text='1/x', width=10, command=lambda: cal('1/x')) bsin = Button(text='sin', width=2, command=lambda: cal('sin')) bcos = Button(text='cos', width=2, command=lambda: cal('cos')) btan = Button(text='tan', width=4, command=lambda: cal('tan')) bpoi = Button(text='.', width=10, command=lambda: appendstr('.')) bequ = Button(text='=', width=2, height=5, command=lambda: cal('=')) # 布局符号按钮 bsub.grid(row=2, column=3) badd.grid(row=1, column=3) bmul.grid(row=3, column=3) bdiv.grid(row=4, column=3) bmod.grid(row=2, column=4) bcon.grid(row=4, column=2) bsin.grid(row=3, column=4) bcos.grid(row=4, column=4) btan.grid(row=1, column=4) bpoi.grid(row=4, column=1) bequ.grid(row=2, column=5, rowspan=3) bdel.grid(row=5, column=0, columnspan=4) bdelall.grid(row=5, column=4, columnspan=4) frame.grid(row=0, column=0, columnspan=10) menubar = Menu(root) root.config(menu=menubar) root.mainloop() |
效果：
当然，计算结果会自动保存到当前目录下的txt文件中去。
