C++ Reference.

Create Tests

#include 
#include 
using namespace std;

void fa();
void fb();
void fc();
void func  ( const int & i );
void func  ( const string & fs );
void func2 ( const string * fs );
void func3 ( const string * fs );
const char * prompt();
int jump   ( const char * );
void (*funcs[])() = { fa, fb, fc, nullptr };


int main( int argc, char ** argv )
{
    int x = 24;
    string s = "Hello";
    puts ("this is main()");
    func(x);

    x = 73;
    printf ("x is %d\n", x);

    func(&s);
    printf ("string is %s\n", s.c_str());
    func2(&s);
    printf ("string2 is %s\n", s.c_str());
    printf ("returned string is %s\n", func3().c_str());

    // function pointer *fp
    void (*fp)() = func4;
    void (*fp)(&s) = &func4; // same as above
    fp(); // or (*fp)();

     while ( jump (prompt()) );
     puts ("\nDone\n");

    fflush(stdout);
    return 0;
}

void func( const int & i )
{
    // would result in error if you try to change i in function
    printf ("value is %d\n", i);
}

void func( const string & fs )
{
    printf ("String is %s\n", fs.c_str());
}

void func2 (const string * fs )
{
    printf ("String2 is %s\n", fs->c_str());
}

// declare to be const so you can't change the string
const string & func3 (const string * fs )
{
    // declare to be static storage so the stack for function won't 
    //    overflow and create security problem
    // auto is deprecated, because it's default and stored in stack
    // stack is created fresh for each function
    //
    // also if you have to return a reference, declare it to be static
    //     so it can be stored in static storage space
    //     auto storage on stack is small. Use reference if you have
    //     to return big object and return the reference in static storage
    static string s = "This is static";
    return s;
}

void func4()
{
    printf ("String2 is %s\n", fs->c_str());
    puts ("a string");
}

void func4(const string * fs)
{
    printf ("String2 is %s\n", fs->c_str());
    puts ("a string");
}

const char * prompt() {

    puts ("Choose an option:");
    puts ("1. do fa()");
    puts ("2. do fb()");
    puts ("Q. quit");
    puts ("Choose an option:");
    printf(">> ");

    fflush(stdout);                // flush after prompt
    const int buffsz = 16;         // constant for buffer size
    static char response [buffsz]; // static storage for response buffer
    fgets(response, buffsz, stdin);// get response from console
    return response;
}

int jump ( const char * rs ) {
    char code = rs[0];
    if (code == 'q' || code == 'Q') return 0;
    // count the length of the funcs array
    int func_length = 0;
    while ( funcs[func_length] != Null ) func_length++;

    int i = (int) code - '0'; // convert ASCII numeral to int
    i--; // list is zero-based
    if ( i < 0 || i >= func_length ) {
        puts ("invalid choice");
        return 1;
    } else {
        funcs[i]();
        return 1;
    }

}