QT_计算器的简单实现

 1  2 //转换为后缀表达式,实现最主要功能
 3 void MainWindow::toPostfix ()
 4 {
 5     QString exp = ui->lineEdit->text ();
 6     //QString exp = "0.3/(5*2+1)", postfix;
 7 
 8     QString tmp = exp;
 9 
10     int j;
11     //如果只有单个数字时
12     for (j = 0; j < tmp.size () && (tmp[j].isDigit () || tmp[j] == '.'); j++) {
13         postFix.push_back (tmp[j]);
14     }
15     if (j == tmp.size ()) {
16         postFix.push_back (' ');
17         return;
18     }
19     postFix.clear ();
20 
21     for (int i = 0; i < exp.size (); i++)
22     {
23         qDebug() << i << exp[i];
24         if (exp[i].isDigit () || exp[i] == '.') {//为数字或者小数点
25             postFix.push_back (exp[i]);          //直接添加到后缀表达式后面
26         }
27         else if (exp[i] == '(') {                //入操作符栈
28             opStack.push (exp[i]);
29         }
30         else if (exp[i] == ')') {                //遇到右括号，就转换成空格添加到后缀表达式中
31             postFix.push_back (' ');
32             while (opStack.top () != '(')
33             {
34                 //只要遇到右括号，则在操作符栈中将栈顶下一次出现'('前的操作符全部依次添加到后缀表达式后面
35                 //因为进栈的时候，是栈顶操作符优先级低;所以出栈的时候，优先级高->低依次添加到后缀表达式后
36                 postFix.push_back (opStack.pop ());
37                 qDebug() << postFix;
38             }
39             opStack.pop ();                     //遇到右括号一次，左括号也相应少一次
40         }
41         //运算符比栈顶的优先级高时，入栈顶
42         else if (getLevel (exp[i]) > getLevel (opStack.top ()))
43         {
44             //将操作符和操作数用空格分开
45             postFix.push_back (' ');
46             opStack.push (exp[i]);
47         }
48         else {
49             postFix.push_back (' '); qDebug() << postFix;
50             //当操作符比栈顶的操作符优先级低时，从栈顶(弹出)pop()运算符，添加到后缀表达式中
51             while (getLevel (exp[i]) <= getLevel (opStack.top ()))
52                 postFix.push_back (opStack.pop ());
53             opStack.push (exp[i]);      //栈顶优先级低则，入栈
54         }
55     }
56     while (opStack.top () != '#') {    //结束标志
57         QChar c = opStack.pop ();
58         postFix.push_back (' ');       //操作符之间用空格分开
59         postFix.push_back (c);         //将栈中剩余的操作符添加到后缀表达式后面
60     }
61     qDebug() << postFix;
62 }

 1 //计算后缀表达式
 2 
 3 void MainWindow::evaluation ()
 4 {
 5     QString tmp;
 6     QStack<double> ans;
 7 
 8     for (int i = 0; i < postFix.size (); i++)
 9     {
10         qDebug() << postFix[i] << i;
11         if (postFix[i].isDigit () || postFix[i] == '.')
12             tmp.push_back (postFix[i]);
13         else if (postFix[i] == ' ') {      //相当于遇到一个操作符或者是括号
14             if (!tmp.isEmpty ())
15             {
16                 ans.push (tmp.toDouble ());
17                 tmp.clear ();
18             }
19             qDebug() << ans.top () << tmp.isEmpty ();
20         }
21         else {       //遇到操作符，从栈中弹出两个数,进行计算，并将结果入栈
22             double a = 0, b = 0;
23             switch (postFix[i].cell ()) {
24             case '!': a = ans.pop ();ans.push (Fac(a)); break;
25 
26             case '+': a = ans.pop (); b = ans.pop ();
27                       ans.push (b + a); break;
28 
29             case '-': a = ans.pop (); b = ans.pop ();
30                       ans.push (b - a); break; //应该是后弹出栈的-先弹出栈的
31 
32             case '*': a = ans.pop (); b = ans.pop ();
33                       ans.push (b * a); break;
34             case '/':a = ans.pop (); b = ans.pop ();
35                      ans.push (b / a); break;
36 
37             case '%': a = ans.pop (); b = ans.pop ();
38                       ans.push ((int)b % (int)a); break;
39 
40             case '^': a = ans.pop (); b = ans.pop ();
41                       ans.push (Pow(b, a)); break;
42             default:
43                 break;
44             }
45             qDebug() << ans.top () << "top";
46         }
47     }
48     ui->lineEdit->setText (QString::number (ans.top ()));
49 }