循环-17. 简单计算器(20)

#include<iostream>
#include<string>
#include<iomanip>
using namespace std;
int main(){
int i=0,flag=0;
float a=0,sum=0;
string str;
char c=' ';
cin>>str;
for(i=0;i<=str.length()-1;++i){
if(i<str.length()-1&&str[i]!='='&&(str[i]=='+'
||str[i]=='-'||str[i]=='*'||str[i]=='/')&&flag){
if(c==' ')
sum=a;
else if(c=='+')
sum+=a;
else if(c=='-')
sum-=a;
else if(c=='*')
sum*=a;
else if(c=='/')
if(a==0){
cout<<"ERROR"<<endl;
break;
}
else
sum/=a;
a=0;
c=str[i];
flag=0;
}
else if(i<str.length()-1&&str[i]>='0'&&str[i]<='9'){
a=a*10+str[i]-'0';
flag=1;
}
else if(i==str.length()-1&&str[i]=='='&&flag){
if(c==' ')
sum=a;
else if(c=='+')
sum+=a;
else if(c=='-')
sum-=a;
else if(c=='*')
sum*=a;
else if(c=='/')
if(a==0){
cout<<"ERROR"<<endl;
break;
}
else
sum/=a;
cout<<fixed<<setprecision(0)<<sum<<endl;
}
else{
cout<<"ERROR"<<endl;
break;
}
}
return 0;
}