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#include <iostream>
#include <cstdlib>
#include <string>
#include <vector>
#include <cmath>
#include <cctype>
using namespace std;
struct Token
{
union
{
char op;
double val;
};
bool isOp;
int rank;
bool isBracket;
int bracket_loc;
};
char rankings[2][3]= { {'^', '*', '+'}, {NULL, '/', '-' } };
char brackets[]= { '(' , ')' , '{', '}', '[', '[', '<' , '>'};
bool isOperand(char c)
{
return (c == '(' || c == ')' || c == '+' || c == '-' || c == '*' || c == '/' || c == '<' || c== '>' || c == '{'
|| c== '}' || c== '[' || c == ']' || c == '^');
}
double solve (char op, double lhs, double rhs)
{
switch (op)
{
case '^':
return pow (lhs,rhs);
case'*':
return lhs*rhs;
case '/':
return lhs/rhs;
case '+':
return lhs+rhs;
case '-':
return lhs-rhs;
default:
cout << "invalid operator" << endl;
break;
}
}
template<typename T>
T get(vector <T> &a)
{
T ret= a.back();
a.pop_back();
return ret;
}
Token val_t(Token &a, int b)
{
a.val=b;
a.isOp=false;
}
Token op_t(Token &a, char b)
{
a.op=b;
a.isOp=true;
for (int i=0; i<2; i++)
{
for (int j=0; j<3; j++)
{
if (b==rankings[i][j])
{
a.rank=j;
}
}
}
for (int i=0; i<8; i++)
{
if (b==brackets[i])
{
a.isBracket=true;
a.bracket_loc=i;
}
}
}
bool isNum(string &a, int i)
{
if (isdigit(a[i]) || a[i]=='.' || (a[i]=='-' && isdigit(a[i+1]) && (!isdigit(a[i-1]) || i==0) ) )
{
return true;
}
return false;
}
vector <Token> tokenize (string &a)
{
vector<Token> ret;
int i=0;
while (i<a.size())
{
if (isNum(a,i))
{
double temp= strtod(a.c_str() + i, 0);
Token buffer;
ret.push_back(val_t(buffer, temp));
while (isNum(a,i))
{
i++;
}
}
else if (isOperand(a[i]) && isNum(a,i-1) && isNum(a,i+1))
{
Token buffer;
ret.push_back(op_t(buffer,a[i]) );
i++;
}
else if (isOperand(a[i]) && (!isOperand(a[i-1]) || (!isOperand(a[i+1]) || i+1==a.size()) ) )
{
cout << "Syntax Error" << endl;
ret.clear();
break;
}
else
{
cout << "Skipping Unknown Character " << a[i] << endl;
i++;
}
}
return ret;
}
int main ()
{
begin:
string equation;
cout << "Please Input equation" << endl;
while (getline(cin,equation))
{
vector <Token> tokens= tokenize(equation);
if(tokens.empty())
{
goto begin;
}
vector<double> values;
vector<char> op;
for (int i=0; i<tokens.size(); i++)
{
if (tokens[i].isBracket)
{
int temp= tokens[i].bracket_loc;
if (tokens[i].bracket_loc%2==1)
{
cout << "Syntax error" <<endl;
goto begin;
}
while (tokens[i].bracket_loc != temp+1 )
{
int rhs=get(values);
int lhs=get(values);
char sign = get(op);
values.push_back(solve(sign,lhs,rhs));
}
i++; // Skips end bracket
}
else if (isOperand(tokens[i].op))
{
op.push_back(tokens[i].op);
if ( (tokens[i].rank >= tokens[i+1].rank) && (i==0 || (tokens[i].rank>tokens[i-1].rank)) )
{
int rhs=get(values);
int lhs=get(values);
char sign = get(op);
values.push_back(solve(sign,lhs,rhs));
}
}
}
while (!op.empty() )
{
int rhs=get(values);
int lhs=get(values);
char sign = get(op);
values.push_back(solve(sign,lhs,rhs));
}
}
}
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