c++计算器

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http://zhidao.baidu.com/link?url=1LOMv7HUIyx6-krghwi0NW-1uRrB1sOrOuCfnMgNgQBp6yjxdotEyAe_WDKZNJs3K1qTcHc76N6_TzmhPdnH9FBOVzVdTT_Z_CcKxUoB1XW

#include<iostream>#include<string>#include<stack>using namespace std; void pop_cal();int p_Rank(char);stack<char> opr_stk;stack<double> num_stk; int main(){    string in_str;    int i=0;    bool num_flag=0;    double x=0;    cout<<"Please input the expression string:"<<endl;    cin>>in_str;    for(i=0;i<in_str.size();i++){        if((in_str[i]>='0')&&(in_str[i]<='9')){            x=x*10+in_str[i]-'0';            num_flag=1;            if(i==in_str.size()-1)                num_stk.push(x);        }        else{            if(x){                num_stk.push(x);                x=0;                num_flag=0;            }            if(opr_stk.empty())                opr_stk.push(in_str[i]);            else if(in_str[i]=='(')                opr_stk.push(in_str[i]);            else if(in_str[i]==')')            {                while(opr_stk.top()!='(')                    pop_cal();                                opr_stk.pop();            }            else if(p_Rank(in_str[i])<=p_Rank(opr_stk.top()))            {                pop_cal();                opr_stk.push(in_str[i]);            }            else{                opr_stk.push(in_str[i]);            }        }    }    while(!opr_stk.empty())        pop_cal();    double res=num_stk.top();    cout<<res<<endl;} void pop_cal(){    char op=opr_stk.top();    double a,b,res;    b=num_stk.top();    num_stk.pop();    a=num_stk.top();    num_stk.pop();    switch(op)    {        case '+':            res=a+b;            break;        case '-':            res=a-b;            break;        case '*':            res=a*b;            break;        case '/':            res=a/b;            break;        default:            break;    }    num_stk.push(res);    opr_stk.pop();} int p_Rank(char x){    if(x=='(')        return 0;    else if(x=='+')        return 1;    else if(x=='-')        return 2;    else if(x=='*')        return 3;    else if(x=='/')        return 4;}

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