string to integer

That is because atoi is expecting a raw const char* pointer. Since there is no implicit conversion from std::string to const char* you get a compiler error. Use c_str() method of std::string to get a c-style const char* for a std::string object. BTW, in C++ you can use streams to do this conversion instead of using these C-style APIs.

atoi(temp.c_str()) 

See these questions:

C atoi() string to int: Points out that atoi() is deprecated.

Why doesn't C++ reimplement C standard functions with C++ elements style?: Gives alternate ways to do what you've listed above.

Well, you passed a std::string (presumably) to atoi, which takes a const char*. Try:

atoi(temp.c_str()); 

which was previously mentioned. Instead, you could use boost's lexical_cast:

std::string temp = "123"; try { int foo = boost::lexical_cast<int>(temp); } catch (boost::bad_lexical_cast e) { //handle error here } 

You could wrap the try/catch into a template function that handles the exceptions in the event that you do not already have exception handling in place.

std::string is not the same as a character pointer (like in C).

int i = 12345; std::string s; std::stringstream sstream; sstream << i; sstream >> s;