test.cpp

#include<cstring> //In C++ with C++ style;
#include<cstdlib> //Includes atoi function;
int main(int argc, char *argv[]) {
  string *s1;
  string *s2;
  int z;
  strlen(s1); // returns length of s1
  strcat(s1,s2); // concatenate s2 to end of s1, s1 then will hold s1+s2
  strcpy(s1,s2); // copy content of s2 into s1, then s2==s1
  strncpy(s1,s2,X); // copy X first character of s2 into s1
  z=atoi(s1); // converts string s1 to int z, atof is used for converting to double and atol is used for converting to long. If string does not have any number then it returns 0
  return 0;
}