Strings

Corus · 01-21-2009, 07:39 PM

What i'm trying to do is, ignore the first 14 digits of the variable w with a string, and use only the other 7, but i've been unsuccessful with my attempts. Could someone explain to me in detail how to fix this or just fix it for me. Here's my original code.

Code:

 #include <iostream>   
 #include <sstream>     
 #include <string>            

using namespace std;
int main() { 
    long double w, t, p;    
    cout << "Please enter the price."; 
    cout << endl;   
    cin>>p;   
    t = 0;   
    cout << "Please scan the the weight.";  
    cin >>w; 
    cout << endl;  
    cout << endl;
    t = w * p + t;
    cout << endl; 
    cout <<"Total:"<<t;
    cout << endl;
    int i = 1000; while (i-- > 0) { cin >> w; t += w * p; cout << endl; cout<<"Total:"<<t; cout << endl; };
    cin.get();
    cin.get();
}

Here's my attempt at fixing it which returned the error:

21 no match for 'operator*' in 'str2 * p'
25 no match for 'operator*' in 'str2 * p'

Code:

 #include <iostream>   /* Declaration */
 #include <sstream>     
 #include <string>            

using namespace std;
int main() { 
    long double t, p;    /* Variables */
    string str2, w;
    cout << "Please enter the price."; /* output */
    cout << endl;   /* next line */
    cin>>p;   /* sets input as p */
    t = 0;   /* sets t as 0 */
    cout << "Please scan the the weight.";  /* output */
    cin >>w; /* input as w */
    cout << endl;  /* next line */
    cout << endl;
    
    string str= w; 
    str2 = str.substr (14,7);

    t = str2 * p + t;
    cout << endl; 
    cout <<"Total:"<<t;
    cout << endl;
    int i = 1000; while (i-- > 0) { cin >> w; t += str2 * p; cout << endl; cout<<"Total:"<<t; cout << endl; };
    cin.get();
    cin.get();
}

Kudose · 01-21-2009, 08:06 PM

I am pretty new to C++, so this may not be the problem ... but ...

It looks like you are trying to multiply a string, which the compiler see as a pointer.

Code:

t = str2 * p + t;

I think you need to cast the string to a double.

tabstop · 01-21-2009, 08:26 PM

I guess the question is, what's wrong with the first 14 digits of w? Is it letters that you need to ignore? If they're all 0, who cares? If they're all numbers that aren't zero, why should you ignore them?

phantomotap · 01-21-2009, 09:23 PM

If the first 14 digits are important enough to ignore and the next 7 digits are important enough to store you probably need to input the value as a string.

If the below example doesn't print '21' the 'double' type isn't going to work.

You need to look at the interface for 'std::string' and 'std::stringstream'. You are trying to get the one to do the job of the other.

Soma

Code:

#include <iostream>
#include <limits>

int main()
{
   typedef std::numeric_limits<double> double_limits;
   if(double_limits::is_bounded)
   {
      std::cout << double_limits::digits10 << '\n';
   }
   else
   {
      std::cout << "unknown";
   }
   return(0);
}

Corus · 01-21-2009, 10:47 PM

None of you had answered my question.

Phantom Map, if you gave me an example of that being used with a cin(So i could get a feel for it), then it would help, also how would i import it as a string?

Tabstop, who cares?

Kudose, how would I do that?

vart · 01-21-2009, 11:15 PM

if you want to convert string to double (after you have cut the instreasting part) - use stringstream

Code:

std::string test("1.23");
std::stringstream stream(test);
double d;
stream >> d;

Kudose · 01-21-2009, 11:45 PM

You should probably use a much more experienced users approach, but the following works.

Code:

#include <iostream>
#include <string>
#include <cstdlib>

using namespace std;

int main(){
	int p = 2;
	string w;
	cin >> w;
	int t;
	const char *cStyle = w.c_str();
	t = atoi(cStyle) * p;
	cout << t;
	return 0;
}

Elysia · 01-22-2009, 02:30 AM

Do I see someone totally ignore the solution vart just gave out?
And corus, start working on that attitude. If someone asks you a question, you can be polite enough to answer; otherwise we are wasting out time helping someone who is rude.

cyberfish · 01-22-2009, 02:55 AM

Quote:

who cares?

Exactly.

Akkernight · 01-22-2009, 03:58 AM

If I understood what cyperfish just said correctly, then hah! Nicely said xD

tabstop · 01-22-2009, 06:44 AM

Quote:

Originally Posted by Corus

Tabstop, who cares?

I don't remember who I'm ripping off (I think bash.org):

Quote:

If we ask you "why do you need to know about jackhammers", and your answer is "so I can open my grandmother's skull and release the demons that are giving her cancer", then maybe teaching you how to use a jackhammer isn't the right thing to do.

In other words, more context may be needed (for instance do you mean 7 digits or 7 characters -- since it's a double there might be a decimal point running loose), etc.

Kudose · 01-22-2009, 10:46 AM

Not that my comments hold water, but vart and Elysia is right.

You should be using the stringstreams (istringstream and ostringstream) in the header file sstream

01-21-2009, 08:06 PM	#2
Kudose Registered User Join Date: Jun 2006 Posts: 72	I am pretty new to C++, so this may not be the problem ... but ... It looks like you are trying to multiply a string, which the compiler see as a pointer. Code: t = str2 * p + t; I think you need to cast the string to a double.
Kudose is offline

01-21-2009, 08:26 PM	#3
tabstop and the Hat of Guessing Join Date: Nov 2007 Posts: 8,740	I guess the question is, what's wrong with the first 14 digits of w? Is it letters that you need to ignore? If they're all 0, who cares? If they're all numbers that aren't zero, why should you ignore them?
tabstop is offline

01-21-2009, 09:23 PM	#4
phantomotap Registered User Join Date: Jan 2008 Posts: 575	If the first 14 digits are important enough to ignore and the next 7 digits are important enough to store you probably need to input the value as a string. If the below example doesn't print '21' the 'double' type isn't going to work. You need to look at the interface for 'std::string' and 'std::stringstream'. You are trying to get the one to do the job of the other. Soma Code: #include <iostream> #include <limits> int main() { typedef std::numeric_limits<double> double_limits; if(double_limits::is_bounded) { std::cout << double_limits::digits10 << '\n'; } else { std::cout << "unknown"; } return(0); }
phantomotap is offline

01-21-2009, 10:47 PM	#5
Corus Registered User Join Date: Jan 2009 Posts: 2	None of you had answered my question. Phantom Map, if you gave me an example of that being used with a cin(So i could get a feel for it), then it would help, also how would i import it as a string? Tabstop, who cares? Kudose, how would I do that?
Corus is offline

01-21-2009, 11:15 PM	#6
vart CSharpener Join Date: Oct 2006 Posts: 5,242	if you want to convert string to double (after you have cut the instreasting part) - use stringstream Code: std::string test("1.23"); std::stringstream stream(test); double d; stream >> d; __________________ If I have eight hours for cutting wood, I spend six sharpening my axe.
vart is offline

01-22-2009, 03:58 AM	#10
Akkernight Hail to the king, baby. Join Date: Oct 2008 Location: Faroe Islands Posts: 714	If I understood what cyperfish just said correctly, then hah! Nicely said xD __________________ I deny the Holy Spirit; burn me. http://blasphemychallenge.com/ <- Do you dare?
Akkernight is offline

01-22-2009, 10:46 AM	#12
Kudose Registered User Join Date: Jun 2006 Posts: 72	Not that my comments hold water, but vart and Elysia is right. You should be using the stringstreams (istringstream and ostringstream) in the header file sstream
Kudose is offline

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