Error in casting

[TheTSPSolver]

I was trying to cast the string to a double in the following program. Unfortunately, I get the following error

========================================================================

1>------ Build started: Project: TimeArb_Simple_1, Configuration: Debug Win32 ------
1>Compiling...
1>Main_1.cpp
1>h:\simple_1\main_1.cpp(22) : error C2065: 'rate1' : undeclared identifier
1>h:\simple_1\main_1.cpp(22) : error C2440: 'type cast' : cannot convert from 'std::string' to 'double'
1>        No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>h:\simple_1\main_1.cpp(23) : error C2065: 'rate2' : undeclared identifier
1>h:\simple_1\main_1.cpp(23) : error C2440: 'type cast' : cannot convert from 'std::string' to 'double'
1>        No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>h:\simple_1\main_1.cpp(24) : error C2065: 'rate1' : undeclared identifier
1>h:\simple_1\main_1.cpp(24) : error C2065: 'rate2' : undeclared identifier
1>h:\simple_1\main_1.cpp(26) : error C2065: 'rate1' : undeclared identifier
1>h:\simple_1\main_1.cpp(26) : error C2065: 'rate2' : undeclared identifier
1>Build log was saved at "file://h:\Simple_1\Debug\BuildLog.htm"
1>TimeArb_Simple_1 - 8 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

========================================================================



My code is below. I tried to cast the sting to a double but it didn't work. Can anyone please help me with this?


======================================================================

#include <iostream>
#include <string>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
using namespace std;

string MaxNum(string r1, string r2);
string irate1;
string irate2;

void main()
{  cout << "Please input the first number" << endl;
   cin >>  irate1;
   cout << "Please input the second number" << endl;
   cin >> irate2;
   cout << irate1 << MaxNum(irate1, irate2) << irate2;
}

string MaxNum(string r1, string r2)
{ 
   rate1 = (double)r1;
   rate2 = (double)r2;
   if(rate1 > rate2)
	   return " is greater than ";
   else if(rate1 < rate2)
	   return " is less than ";
   else
       return " is equal to ";
}

======================================================================

[TheTSPSolver]

BTw, in the above code, I tried using atof as well but it didn't work.

[Castaway]

You need to initialize variables rate1 and rate2 in MaxNum(). Also, when atof() takes a const char* as parameter, so you need to extract it from the string object. For example:

double rate1 = atof(r1.c_str());
double rate2 = atof(r1.c_str());

Also, the return type of main() must be int.

[TheTSPSolver]

Thank you so much for your help.

[packetpirate]

Why are you storing double numbers in a string anyway? You do realize that just because your function is of type string, that doesn't mean the parameters have to be strings, too... if you're passing in a value that's of type double, use DOUBLE parameters... and if you want to return a value, make sure that value is of the same type as the function!

Here's a better way to do what you're doing...

#include <iostream>
using std::cout;
using std::cin;
using std::endl;

void biggerNum(double first, double second);

int main()
{

    double first, second;
    cout << "What are the two numbers? ";
    cin >> first >> second;

    biggerNum(first, second);

    return 0;
}

void biggerNum(double first, double second)
{
    if(first > second)
    {
        cout << first << " is greater than " << second << "." << endl;
    }
    else if(first < second)
    {
        cout << first << " is less than " << second << "." << endl;
    }
    else if(first == second)
    {
        cout << first << " is equal to " << second << "." << endl;
    }
    else
    {
        cout << "Invalid input." << endl;
    }
}

Also, don't use global variables :(