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what's wrong with this program?

6 New Member
I am getting the error:
[Error] 'atoi' was not declared in this scope
Expand|Select|Wrap|Line Numbers
  1. #include <iostream>
  2.       #include <string.h>
  4.        using namespace std;
  5.        int main()
  6.        {
  7.            string str = "131.90";
  8.         int n;
  9.            n = atoi(str);
  10.            cout << n;
  11.            return 0;
  12.        }
Jan 12 '14
13 46682
4 New Member
Zee Malik,
I am also not expert in C++. If I know something on it, definitely I will share with you.
Jan 13 '14 #11
9,065 Recognized Expert Moderator Expert
You should only really call a function like .c_str if you need to call a legacy C function. In this case atoi is a legacy C function but C++ has plenty of better options that you could use (actually the legacy C standard library has better options to use other than atoi). In a good C++ design you should be avoiding dropping down to C constructs like arrays if at all possible favouring vector<> or array<> instead.

This can be implemented entirely using the C++ library using a stringstream which has the advantage that you cen tell how much of the string has been converted.

Expand|Select|Wrap|Line Numbers
  1. #include<iostream>
  2. #include<string>
  3. #include<sstream>
  5. using namespace std;
  7. int main()
  8. {
  9.   string str = "131.90";
  10.   string leftover;
  11.   istringstream iss;
  12.   int result;
  14.   iss.str(str);
  16.   iss >> result;
  17.   iss >> leftover;
  19.   cout << "Converted: " << result << " Leftover: " << leftover << endl;
  20. }
Output: Converted: 131 Leftover: .90

By simply changing the type of result to double I can convert the whole string.
Jan 13 '14 #12
4 New Member
I can convert whole string in one line.

Expand|Select|Wrap|Line Numbers
  1.     #include <iostream>
  2.     #include <string.h>
  4.     using namespace std;
  6.      int main()
  7.      {
  8.        string str= "131.90";
  9.        int n;
  10.        n=stoi(str);
  11.        cout<<n;
  12.      }
stoi() converts string to integer.
Its better & easy to use compare to atoi() & c_str() & iss.str().

Don't forget to run like this : g++ -std=c++0x ............
Jan 14 '14 #13
9,065 Recognized Expert Moderator Expert
You are correct, I overlooked this because it is part of C++11 (and extensions on some compilers) and I am not altogether familiar with C++11 yet as my project is still using C++98
Jan 14 '14 #14

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