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#include <iostream>
#include <string>
#include <stdlib.h>
#include <sstream>
using namespace std;
bool isOperator(char ch)
{
return (ch == '+') ||
(ch == '-') ||
(ch == '*') ||
(ch == '/');
}
bool isHigherPrior(char ch)
{
return (ch == '/') ||
(ch == '*');
}
bool isOperand(char ch)
{
return ('0' < ch && ch < '9');
}
bool isLeftParen(char ch)
{
return (ch == '(');
}
bool isRightParen(char ch)
{
return (ch == ')');
}
string arrange(string str)
{
for(unsigned int i=0; i<str.size(); i++)
{
if(str[i] == ' ') // delete space
{
str.erase(i, 1);
i--;
}
if(str[i] == '+' && isOperator(str[i-1])) // delete unary plus
{
str.erase(i, 1);
i--;
}
}
for(unsigned int i=0; i<str.size(); i++)
{
if((isLeftParen(str[i]) && isRightParen(str[i+1])) || (isRightParen(str[i]) && isLeftParen(str[i+1]))) // delete case () and )(
{
str.erase(i, 2);
i=i-2;
}
if(isOperator(str[i]) && isOperator(str[i+1]))
{
if(str[i]=='-' && str[i+1]=='-') // -- = +
{
str.erase(i, 2);
str.insert(i, "+");
i--;
}
else if(str[i]=='+' && str[i+1]=='-') // +- = -
{
str.erase(i, 2);
str.insert(i, "-");
i--;
}
}
}
return str;
}
bool checkValidity(string str, int &paren)
{
bool valid = true;
int left=0, right=0;
arrange(str);
if(isOperator(str[str.size()-1]) || isHigherPrior(str[0])) // *, / at the first string or any operator at last => error
valid = false;
for(unsigned int i=0; i<str.size(); i++)
{
if(isLeftParen(str[i])) // count left parenthesis
{
if(isOperand(str[i-1]) || isRightParen(str[i+1])) // number( or () => error
{
valid = false;
break;
}
left++;
}
if(isRightParen(str[i])) // count right parenthesis
{
if(isOperand(str[i+1])) // )number => error
{
valid = false;
break;
}
right++;
}
if(isOperator(str[i]) && isHigherPrior(str[i+1])) // +/ or -* ... => error
{
valid = false;
break;
}
if(!isOperand(str[i]) && !isOperator(str[i]) && !isLeftParen(str[i]) && !isRightParen(str[i]) && str[i]!='.') // letter => error
{
valid = false;
break;
}
}
if(left != right){ // left parenthesis != right => error
valid = false;
}
if(valid == false) // invalid
{
cout << "Expression is invalid" << endl;
return false;
}
else // valid, number of parenthesis = left parenthesis
{
paren = left;
return true;
}
}
double eval(string str, int num)
{
int posL, posR;
while(num>0) // recursive to evaluate in (...);
{
posR = str.find(")");
posL = str.rfind("(", posR);
string temp = str.substr(posL+1, posR-posL-1);
double t = eval(temp, 0);
stringstream ss;
ss << t;
str.replace(posL, posR-posL+1, ss.str());
str = arrange(str);
num--;
}
double left, right;
unsigned int j;
for(j=0; j<str.size(); j++)
{
if(isHigherPrior(str[j])) // evaluate * / first and + -
{
unsigned int l;
for(l=j-1; l>=0; l--) // take left operator
if(isOperator(str[l]))
break;
if(l == 0) // unary minus e.g: (-3)
{
left = atof(str.substr(l, j-l).c_str());
str.erase(l, 1);
l--;
j--;
}
else
left = atof(str.substr(l+1, j-l-1).c_str());
if(str[l] == '-' && isOperator(str[l-1])) // unary minus
{
left = -1*left;
str.erase(l-1, 1);
l--;
j--;
}
unsigned int k;
for(k=j+1; k<str.size(); k++) // take right operator
if(isOperator(str[k]))
break;
if(isOperator(str[j+1])) // unary minus
{
str.erase(j+1, 1);
for(k=j+1; k<str.size(); k++)
if(isOperator(str[k]))
break;
right = -1*atof(str.substr(j+1, k-j-1).c_str());
}
else
right = atof(str.substr(j+1, k-j-1).c_str());
switch(str[j])
{
case '*':
{
double t = left * right;
stringstream ss;
ss << t;
str.replace(l+1, k-l-1, ss.str());
break;
}
case '/':
{
double t = left / right;
stringstream ss;
ss << t;
str.replace(l+1, k-l-1, ss.str());
break;
}
}
j=-1;
}
}
str = arrange(str);
for(unsigned int i=0; i<str.size(); i++) // + -
{
if(isOperand(str[i]))
{
unsigned int l; // take left operator
for(l=i; l<str.size(); l++)
if(isOperator(str[l]))
break;
if(l==str.size())
break;
left = atof(str.substr(i, l-i).c_str());
if(str[i-1] == '-')
{
left = -1*left;
str.erase(i-1, 1);
i--;
l--;
}
unsigned int k; // take right operator
for(k=l+1; k<str.size(); k++)
if(isOperator(str[k]))
break;
right = atof(str.substr(l+1, k-l-1).c_str());
switch(str[l])
{
case '+':
{
double t = left + right;
stringstream ss;
ss << t;
str.replace(i, k-i, ss.str());
break;
}
case '-':
{
double t = left - right;
stringstream ss;
ss << t;
str.replace(i, k-i, ss.str());
break;
}
}
i=-1;
}
}
double t = atof(str.c_str());
str = "";
return t;
}
int main()
{
// (3- - 2) + (4 -3 ) - - 4 = 10
// 3 +2 -- ++ ( 2.4 - 4.4 ) -4 * 3 = -9
// ((((3-4*2)* 2.2 + 3* (-4.4-2))-2.1)/-2)-1() = 15.15
// 3(3+2) : *error
// (2-3)3 : *error
// ** or // or +* ... : *error
string str;
int paren = 0;
cout << "Input an infix arithmetic expression:" << endl;
getline(cin, str);
str = arrange(str);
if(checkValidity(str, paren))
cout << "The result is: " << eval(str, paren) << endl;
return 0;
}
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