hello, I am writing a variable equation solver. Now to get it to work, i just need your calculator to be able to detect random strings instead of numbers. and when it does, i need to assign a random number to that string and have the calculator solve the problem again with that new number. I am also wondering how to get your calculator to detect ( and ) so it can solve problems like (1+1)*(1+1). thanks

here, i finished a normal calculator that can handle paranthesis, order of operations, and unlimited operators.

#include<iostream>
#include<string>
#include<sstream>
#include<windows.h>
#include<conio.h>
#include<ctime>
using namespace std;
int main ()
{
    cout << "No variables." << endl;
    cout << "Type in cls to clear the screen, and type exit to exit." << endl;
    SetConsoleTitle("Calculator");
    for(;;)
    {
    re:
    string equation = "";
    string equation2 = "";
    string equation3 = "";
    string equation4 = "";
    string equation5 = "";
    int non_digit5 = 0;
    int non_digit2 = -1;
    int non_digit6 = 0;
    int c = 0;
    int i = 0;
    float n1 = 0;
    string operators = "";
    float n2 = 0;
    cin >> equation;
    DWORD ticks = GetTickCount();
    if(equation == "exit")
    {
                return 0;
    }
    
    if(equation == "cls")
    {
                system("cls");
                goto re;
    }
    while(true)
    {
               c = equation.find('(', c);
               if(c == -1)
               {
                    break;
               }
    //PARENTHESIS SOLVING CODE
    do
    {
                  non_digit2 = equation.find('(', non_digit2+1);
                  if(non_digit2 == -1)
                  {
                        break;
                  }
                  non_digit5 = non_digit2;
    }while(non_digit2 != -1);
    non_digit5 = non_digit5 + 1;
    int non_digit3 = 0;
    //DOUBLE PARANTHESIS EQUATIONS
    equation4 = equation.substr(non_digit5, 999999999);
    int l = equation.length();
    int l1 = equation4.length();
    non_digit3 = equation4.find(")", non_digit3+1);
    l1 = l1 - non_digit3;
    l = l - l1;
    non_digit3 = l;
    equation3 = equation.substr(non_digit3+1, 999999999);
    equation2 = equation.substr(non_digit5, non_digit3);
    do
    {
                  non_digit2 = equation2.find(')', non_digit2+1);
                  if(non_digit2 == -1)
                  {
                        break;
                  }
                  non_digit6 = non_digit2;
    }while(non_digit2 != -1);
    equation2 = equation2.substr(0, non_digit6);
    equation = equation.substr(0, non_digit5-1);
    n1 = 0;
    operators = "";
    n2 = 0;
    int non_digit = equation2.find_first_not_of("12345677890.");
    string part = equation2.substr(0, non_digit);
    stringstream(part) >> n1;
    operators = equation2[non_digit];
    equation2 = equation2.substr(non_digit + 1);
    while(true)
    {
             n2 = 0;
             non_digit = equation2.find_first_not_of("1234567890.");
             part = equation2.substr (0, non_digit);
             stringstream(part) >> n2;
             if(int(non_digit) == 0)
             {
                               string part = equation2.substr (0, non_digit+3);
                               stringstream(part) >> n2;
                               equation2 = equation2.substr(non_digit + 1);
             }
        if(operators == "+")
        {
                     n1 = n1 + n2;   
        }      
        
        if(operators == "-")
        {
                     n1 = n1 - n2;
        }
        
        if(operators == "*")
        {
                     n1 = n1 * n2; 
        }
        
        if(operators == "/")
        {
                     n1 = n1 / n2;
        }
        
        if(non_digit == -1)
        {
                           break;
        }
        non_digit = equation2.find_first_not_of("0123456789.");
        operators = equation2[non_digit];
        equation2 = equation2.substr(non_digit + 1);
    }
        stringstream out;
        out << n1;
        equation = equation + out.str();
        equation = equation + equation3;
    }
    //ORDER OF OPERATIONS
    while(true)
    {
               c = equation.find_first_not_of("1234567890.-+");
               if(c == -1)
               {
                    break;
               } 
    equation2 = "";
    equation3 = "";
    equation4 = "";
    operators = "";
    float n1 = 0;
    float n2 = 0;
    float n3 = 0;
    int non_digit = equation.find_first_not_of("1234567890.-+");
    operators = equation[non_digit];
    equation2 = equation.substr(non_digit+1, 999999999);
    stringstream(equation2) >> n1;
    equation3 = equation.substr(0,non_digit);
    reverse(equation3.begin(), equation3.end());
    //BEGIN FIXING REVERSED EQUATION
    non_digit = equation3.find_first_not_of("1234567890.");
    if(non_digit == -1)
    {
                 reverse(equation3.begin(), equation3.end());
                 stringstream(equation3) >> n2;
    }
    else
    {
                 equation5 = equation3.substr(0, non_digit);
                 reverse(equation5.begin(), equation5.end());
                 stringstream(equation5) >> n2;
    }
    
    stringstream out;
    out << n2;
    equation4 = equation4 + out.str();
    equation4 = equation4 + operators;
    stringstream out1;
    out1 << n1;
    equation4 = equation4 + out1.str();
    //END OF FIND OPERATOR
    int l = equation4.length();
    non_digit = equation.find(equation4);
    equation2 = equation.substr(0, non_digit);
    equation4 = equation.substr(non_digit+l, 999999999);
    if(operators == "/")
    {
                 n3 = n2 / n1;
    }
    if(operators == "*")
    {
                 n3 = n2 * n1;
    }
    stringstream out2;
    out2 << n3;
    equation2 = equation2 + out2.str();
    equation2 = equation2 + equation4;
    equation = equation2;
    }
    //START FIXED EQUATION SOLVING
    n1 = 0;
    operators = "";
    n2 = 0;
    size_t non_digit = equation.find_first_not_of("12345677890.");
    string part = equation.substr (0, non_digit);
    stringstream(part) >> n1;
    operators = equation[non_digit];
    equation = equation.substr(non_digit + 1);
    while (true)
    {
             n2 = 0;
             size_t non_digit = equation.find_first_not_of("1234567890.");
             string part = equation.substr (0, non_digit);
             stringstream(part) >> n2;
             if(int(non_digit) == 0)
             {
                               string part = equation.substr (0, non_digit+3);
                               stringstream(part) >> n2;
                               equation = equation.substr(non_digit + 1);
             }
        if(operators == "+")
        {
                     n1 = n1 + n2;   
        }      
        
        if(operators == "-")
        {
                     n1 = n1 - n2;
        }
        
        if(operators == "*")
        {
                     n1 = n1 * n2; 
        }
        
        if(operators == "/")
        {
                     n1 = n1 / n2;
        }
        
        if (int(non_digit) == -1)
        {
                           break;
        }
        
        non_digit = equation.find_first_not_of("0123456789.");
        operators = equation[non_digit];
        equation = equation.substr(non_digit + 1);
    }
    cout << "Speed of calculation: " << GetTickCount() - ticks << " milliseconds." << endl;
    cout << "Result : " << n1 << endl;
    system("pause");
    goto re;
    }
}
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