Namespaces provide a method for preventing name conflicts in large projects. Symbols declared inside a namespace block are placed in a named scope that prevents them from being mistaken for identically-named symbols in other scopes. Multiple namespace blocks with the same name are allowed. All declarations within those blocks are declared in the named scope.
Here we present the C++ version without using namespace.
// A comment line begins like this in C++ programs
// Standard ANSI-C++ include files
#include <iostream> // input and output
#include <cmath> // math functions
using namespace std;
int main (int argc, char* argv[])
{
// convert the text argv[1] to double using atof:
double r = atof(argv[1]); // convert the text argv[1] to double
double s = sin(r);
// Note std::cout and std::endl
std::cout << "Hello, World! sin(" << r << ") =" << s << std::endl;
return 0; // success execution of the program
}