#include <QChar>
#include <QStack>
static double opTwoOprand(QChar op,double s2,double s1){
switch (op.toLatin1()) {
case '+':
return s1 + s2;
case '-':
return s2 - s1;
case '*':
return s2 * s1;
case '/':
return s2 / s1;
default:
return 0;
}
}
double evalExpresion(QString expr){
QStack<QChar> opcode;
QStack<double> oprand;
for(int i=0;i<expr.length();){
if(QChar::isDigit(expr[i].toLatin1())){
QString oprandStr;
oprandStr.append(expr[i]);
while(++i<expr.length()&&(QChar::isDigit(expr[i].toLatin1())||QChar::fromLatin1('.')==expr[i])){
oprandStr.append(expr[i]);
}
oprand.push(oprandStr.toDouble());
}else{
QChar op;
if(!opcode.isEmpty()){
op= opcode.top();
}
QChar iop = expr[i];
switch (iop.toLatin1()){
case '+':
case '-':
if(!op.isNull()&&(
op == QChar::fromLatin1('*') || op == QChar::fromLatin1('/')||
op == QChar::fromLatin1('+') || op == QChar::fromLatin1('-')
)){
double s1 = oprand.pop();
double s2 = oprand.pop();
oprand.push(opTwoOprand(op,s2,s1));
opcode.pop();
}
opcode.push(iop);
break;
case '*':
case '/':
if(!op.isNull()&&(op == QChar::fromLatin1('*') || op == QChar::fromLatin1('/'))){
double s1 = oprand.pop();
double s2 = oprand.pop();
oprand.push(opTwoOprand(op,s2,s1));
opcode.pop();
}
opcode.push(iop);
break;
case '(':
opcode.push(iop);
break;
case ')':
if(!op.isNull()){
op = opcode.pop();
if(op == QChar::fromLatin1('*') || op == QChar::fromLatin1('/')){
double s1 = oprand.pop();
double s2 = oprand.pop();
oprand.push(opTwoOprand(op,s2,s1));
op = opcode.pop();
}
QStack<QChar> opcodeReverse;
QStack<double> oprandReverse;
while(op != QChar::fromLatin1('(')){
opcodeReverse.push(op);
oprandReverse.push(oprand.pop());
op = opcode.pop();
}
if(!opcodeReverse.isEmpty()){
oprandReverse.push(oprand.pop());
do{
op = opcodeReverse.pop();
double s1 = oprandReverse.pop();
double s2 = oprandReverse.pop();
oprandReverse.push(opTwoOprand(op,s1,s2));
}while(!opcodeReverse.isEmpty());
oprand.push(oprandReverse.pop());
}
}
break;
}
i++;
}
}
QStack<QChar> opcodeReverse;
QStack<double> oprandReverse;
while(!oprand.isEmpty()){
oprandReverse.push(oprand.pop());
}
while(!opcode.isEmpty()){
opcodeReverse.push(opcode.pop());
}
do{
QChar op = opcodeReverse.pop();
double s1 = oprandReverse.pop();
double s2 = oprandReverse.pop();
oprandReverse.push(opTwoOprand(op,s1,s2));
}while(!opcodeReverse.isEmpty());
return oprandReverse.top();
}
