Exercise with array of pointers to func

Hi,

I have the following code:

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#include <iostream>
using namespace std;

// A macro to define dummy functions:
#define DF(N) void N() { \
   cout << "function " #N " called..." << endl; }

DF(a); DF(b); DF(c); DF(d); DF(e); DF(f); DF(g);

void ((*(func_table[]))()) = { &a, &b, &c, &d, &e, &f, &g };

int main() {
  while(1) {
    cout << "press a key from 'a' to 'g' "
      "or q to quit" << endl;
    char c, cr;
    cin.get(c); cin.get(cr); // second one for CR
    if ( c == 'q' )
      break; // ... out of while(1)
    if ( c < 'a' || c > 'g' )
      continue;
    (*(func_table[c - 'a']))();
  }
}
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and I am supposed to make the functions a(), b(), ... return a string and
print the string in the main(). I initially thought that nothing's more
simple, that I just needd some replacements, like:

--------------------------------------------------------------------------------------
#include <iostream>
using namespace std;

// A macro to define dummy functions:
#define DF(N) string N() { \
    return "function " #N " called..."; }

DF(a); DF(b); DF(c); DF(d); DF(e); DF(f); DF(g);

string ((*(func_table[]))()) = { &a, &b, &c, &d, &e, &f, &g };

int main() {
  while(1) {
    cout << "press a key from 'a' to 'g' "
      "or q to quit" << endl;
    char c, cr;
    cin.get(c); cin.get(cr); // second one for CR
    if ( c == 'q' )
      break; // ... out of while(1)
    if ( c < 'a' || c > 'g' )
      continue;
    cout << ((*(func_table[c - 'a']))()) << endl;
  }
}
--------------------------------------------------------------------------------------

But the compiler doesn't agree.

If I substitute

    cout << ((*(func_table[c - 'a']))()) << endl;

by

    string str=((*(func_table[c - 'a']))());
    cout << str << endl;

the first error spoted is still on the cout (I just wanted to make sure the
tricky expression is a real real string even if the compiler says that:
binary '<<' : no operator found which takes a right-hand operand of type
'std::string')

But if I try with a constand string like "hello", it works.
Do you know why?

Do you know how should I do to print the string returned by my functions?

Thank you