四则运算表达式求值

#include<iostream>

#include<cstring>
#include<cstdlib>
using namespace std;
int biaodashi();
int xiang();
int yinzi();
int main()
{
cout<<biaodashi()<<endl;
system("pause");
return 0;
}
int biaodashi()
{
int result=xiang();
bool more=true;
while(more){
char op=cin.peek();
if(op=='+'||op=='-'){
cin.get();
int value=xiang();
if(op=='+') result+=value;
else result-=value;
}
else more=false;
}
return result;
}
int xiang()
{
int result=yinzi();
while(true){
char op=cin.peek();
if(op=='*'||op=='/'){
cin.get();
int value=yinzi();
if(op=='*')
result*=value;
else result/=value;
}
else break;
}
return result;
}
int yinzi()
{
int result=0;
char c=cin.peek();
if(c=='('){
cin.get();
result=biaodashi();
cin.get();
}
else{
while(isdigit(c)){//判断是否是数字
result=10*result+c-'0';
cin.get();
c=cin.peek();
}
}
return result;
}