Thread: simple program for char-int

Originally Posted by ziga

prog-bman thx for the link i was searching thrue librarys and found a function
string ( const string& str, size_t pos, size_t n = npos )

a string isn't a function, its the data type in C++ which is used to represent string data (You might have been using char arrays up til now - but C++ strings are a far better way)

it works just like i wanted it even displays + or - if i put it in.
but now if i wanna transform those digits in to numbers using atoi function i cant??
why wont it work.
or is there any other way to transform a std::string to integer

Code:

#include <iostream>
#include <string>
using namespace std;

int main ()
{

string s5;
int a;
cout <<" iput string  ";
cin>> s5;
  string s3 (s5, 8, 3);

a = atoi (s3);
  cout << "ns3: " << s3<<endl;
cout << " a =  " << a <<endl;
  return 0;
}

Don't use atoi - its unsafe, you can't reliably check for a valid conversion, which can lead to all sorts of problems.

C++ has a facility called stringstreams which will do what you're after safely

Code:

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

int main()
{
    std::string str;
    std::cout << "Enter a number: ";
    std::getline(std::cin, str);

    std::stringstream ss;
    ss << str << 83;

    int i;
    if ( ss >> i )
        std::cout << "Valid conversion to int: " << i;
    else
        std::cout << "Invalid input";
}

ok i didnt see youre post bench82 i just posted what ive been doing this morning ill try your program.
I have a question what is the diference between std::cout and only cout"...?
were can i find more data on std::stringstream
http://www.cplusplus.com/reference/i.../stringstream/
i gues this is not it?

>> if i input a string:
>> 2345687 h 15432
>> i am not able to get numbers a = 2345 and b = 5432

In your original example there were separators between the numbers. If you want to read in 2345687 as 2345, then you have to do special processing, because 2345687 is 2345687.

Are you saying that the numbers are always at most 4 digits? You have to have rules that define what the numbers will be, or else you cannot write code to enforce the rules.

If what you want is to read in at most 4 digits into your number, then you should read in 4 digits into a string, then convert that string to an int. You still only need a single int per number.

As far as atoi or stringstream, I prefer stringstreams, too, but either will work and you should be focusing on the other parts of the program.

Also, this code:

Code:

cstr = new char [s4.size()+1];
strcpy (cstr, s4.c_str());
a = atoi (cstr);

should be changed to this:

Code:

a = atoi (s4.c_str());