How to declare function using reference? - c++

Question

I am making this program to check the alphabetic and numeric characters of a C-type string. I am using C-type strings because it is for an assignment, otherwise I would opt to use std::string.
How do I declare the function? In my case, I want str, SAlpha and SNum, to be stored in the function as s, alpha, num. That's why I am using references, but I don't understand how to declare it without giving me an error saying undefined.
I have been searching, but I am new to functions, and don't understand them quite well. That's why I'm asking.
Below is the code:
#include <iostream>
#include <cstring>
#include <cctype>
using namespace std;
void seperate(char (&s)[], char (&alpha)[], char (&num)[]);
int main() {
char str[100];
char SAlpha[100];
char SNum[100];
cout << "Insert a string: ";
cin.getline(str,100);
strcpy(SAlpha, str);
strcpy(SNum,str);
cout << "Alphabetic characters " << endl;
for (int i = 0; i < strlen(SAlpha); i++) {
if (isalpha(SAlpha[i])) {
cout << " " << SAlpha[i];
}
}
cout << endl;
cout << "Numeric characters " << endl;
for (int i = 0; i < strlen(SNum);i++) {
if (isdigit(SNum[i])) {
cout << " " << SNum[i];
}
}
seperate(str, SAlpha, SNum); //UNDEFINED FUNCTION
return 0;
}

Answer 1

You are getting an "undefined" error because you have only declared the seperate() function but have not implemented it yet, eg:
#include <iostream>
#include <cstring>
#include <cctype>
using namespace std;
// THIS IS JUST A DECLARATION!!!
void seperate(char (&s)[100], char (&alpha)[100], char (&num)[100]);
int main() {
char str[100];
char SAlpha[100];
char SNum[100];
cout << "Insert a string: ";
cin.getline(str,100);
strcpy(SAlpha, str);
strcpy(SNum,str);
cout << "Alphabetic characters " << endl;
for (int i = 0; i < strlen(SAlpha); i++) {
if (isalpha(SAlpha[i])) {
cout << " " << SAlpha[i];
}
}
cout << endl;
cout << "Numeric characters " << endl;
for (int i = 0; i < strlen(SNum);i++) {
if (isdigit(SNum[i])) {
cout << " " << SNum[i];
}
}
seperate(str, SAlpha, SNum); // <-- OK TO CALL SINCE THE FUNCTION IS DECLARED ABOVE...
return 0;
}
// ADD THIS DEFINITION!!!
void seperate(char (&s)[100], char (&alpha)[100], char (&num)[100])
{
// do something here...
}