int a =123;
char buf[100];
sprintf(buf,"%d", a);
string s = buf; 

string s = "123";
sscanf(s.c_str(),"%d", &a); 

int a =123;
double d = 123.4567;
string s = "strings";
char buf[100];
sprintf(buf,"%s = %d / %.2lf", s.c_str(), a, d);
s = buf; 

 
#include <sstream>
using namespace std;
...
int a;
string s;
// int->string
a = 47;
ostringstream os;
os << a;
s = os.str();
// string->int
s = "74";
istringstream is(s);
is >> a;
 

	string ss = "124";
	int x = atoi(ss.c_str());