qt_计算器的简单实现

  //转换为后缀表达式,实现最主要功能
 void MainWindow::toPostfix ()
 {
     QString exp = ui->lineEdit->text ();
     //QString exp = "0.3/(5*2+1)", postfix;

     QString tmp = exp;

     int j;
     //如果只有单个数字时
     for (j = ; j < tmp.size () && (tmp[j].isDigit () || tmp[j] == '.'); j++) {
         postFix.push_back (tmp[j]);
     }
     if (j == tmp.size ()) {
         postFix.push_back (' ');
         return;
     }
     postFix.clear ();

     for (int i = ; i < exp.size (); i++)
     {
         qDebug() << i << exp[i];
         if (exp[i].isDigit () || exp[i] == '.') {//为数字或者小数点
             postFix.push_back (exp[i]);          //直接添加到后缀表达式后面
         }
         else if (exp[i] == '(') {                //入操作符栈
             opStack.push (exp[i]);
         }
         else if (exp[i] == ')') {                //遇到右括号，就转换成空格添加到后缀表达式中
             postFix.push_back (' ');
             while (opStack.top () != '(')
             {
                 //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
                 //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
                 postFix.push_back (opStack.pop ());
                 qDebug() << postFix;
             }
             opStack.pop ();                     //遇到右括号一次，左括号也相应少一次
         }
         //运算符比栈顶的优先级高时，入栈顶
         else if (getLevel (exp[i]) > getLevel (opStack.top ()))
         {
             //将操作符和操作数用空格分开
             postFix.push_back (' ');
             opStack.push (exp[i]);
         }
         else {
             postFix.push_back (' '); qDebug() << postFix;
             //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
             while (getLevel (exp[i]) <= getLevel (opStack.top ()))
                 postFix.push_back (opStack.pop ());
             opStack.push (exp[i]);      //栈顶优先级低则，入栈
         }
     }
     while (opStack.top () != '#') {    //结束标志
         QChar c = opStack.pop ();
         postFix.push_back (' ');       //操作符之间用空格分开
         postFix.push_back (c);         //将栈中剩余的操作符添加到后缀表达式后面
     }
     qDebug() << postFix;
 }

 //计算后缀表达式

 void MainWindow::evaluation ()
 {
     QString tmp;
     QStack<double> ans;

     for (int i = ; i < postFix.size (); i++)
     {
         qDebug() << postFix[i] << i;
         if (postFix[i].isDigit () || postFix[i] == '.')
             tmp.push_back (postFix[i]);
         else if (postFix[i] == ' ') {      //相当于遇到一个操作符或者是括号
             if (!tmp.isEmpty ())
             {
                 ans.push (tmp.toDouble ());
                 tmp.clear ();
             }
             qDebug() << ans.top () << tmp.isEmpty ();
         }
         else {       //遇到操作符，从栈中弹出两个数,进行计算，并将结果入栈
             double a = , b = ;
             switch (postFix[i].cell ()) {
             case '!': a = ans.pop ();ans.push (Fac(a)); break;

             case '+': a = ans.pop (); b = ans.pop ();
                       ans.push (b + a); break;

             case '-': a = ans.pop (); b = ans.pop ();
                       ans.push (b - a); break; //应该是后弹出栈的-先弹出栈的

             case '*': a = ans.pop (); b = ans.pop ();
                       ans.push (b * a); break;
             case '/':a = ans.pop (); b = ans.pop ();
                      ans.push (b / a); break;

             case '%': a = ans.pop (); b = ans.pop ();
                       ans.push ((int)b % (int)a); break;

             case '^': a = ans.pop (); b = ans.pop ();
                       ans.push (Pow(b, a)); break;
             default:
                 break;
             }
             qDebug() << ans.top () << "top";
         }
     }
     ui->lineEdit->setText (QString::number (ans.top ()));
 }

//全部代码见，百度云

链接: https://pan.baidu.com/s/1qXQKPTM 密码: qwfn