C++ function not found during compilation - c++

Question

For a homework assignment: I'm supposed to create randomized alphabetial keys, print them to a file, and then hash each of them into a hash table using the function "goodHash", found in my below code.
When I try to run the below code, it says my "goodHash" "identifier isn't found". What's wrong with my code?
#include <iostream>
#include <vector>
#include <cstdlib>
#include "math.h"
#include <fstream>
#include <time.h>
using namespace std;
// "makeKey" function to create an alphabetical key
// based on 8 randomized numbers 0 - 25.
string makeKey() {
int k;
string key = "";
for (k = 0; k < 8; k++) {
int keyNumber = (rand() % 25);
if (keyNumber == 0)
key.append("A");
if (keyNumber == 1)
key.append("B");
if (keyNumber == 2)
key.append("C");
if (keyNumber == 3)
key.append("D");
if (keyNumber == 4)
key.append("E");
if (keyNumber == 5)
key.append("F");
if (keyNumber == 6)
key.append("G");
if (keyNumber == 7)
key.append("H");
if (keyNumber == 8)
key.append("I");
if (keyNumber == 9)
key.append("J");
if (keyNumber == 10)
key.append("K");
if (keyNumber == 11)
key.append("L");
if (keyNumber == 12)
key.append("M");
if (keyNumber == 13)
key.append("N");
if (keyNumber == 14)
key.append("O");
if (keyNumber == 15)
key.append("P");
if (keyNumber == 16)
key.append("Q");
if (keyNumber == 17)
key.append("R");
if (keyNumber == 18)
key.append("S");
if (keyNumber == 19)
key.append("T");
if (keyNumber == 20)
key.append("U");
if (keyNumber == 21)
key.append("V");
if (keyNumber == 22)
key.append("W");
if (keyNumber == 23)
key.append("X");
if (keyNumber == 24)
key.append("Y");
if (keyNumber == 25)
key.append("Z");
}
return key;
}
// "makeFile" function to produce the desired text file.
// Note this only works as intended if you include the ".txt" extension,
// and that a file of the same name doesn't already exist.
void makeFile(string fileName, int n) {
ofstream ourFile;
ourFile.open(fileName);
int k; // For use in below loop to compare with n.
int l; // For use in the loop inside the below loop.
string keyToPassTogoodHash = "";
for (k = 1; k <= n; k++) {
for (l = 0; l < 8; l++) { // For-loop to write to the file ONE key
ourFile << makeKey()[l];
keyToPassTogoodHash += (makeKey()[l]);
}
ourFile << " " << k << "\n";// Writes two spaces and the data value
goodHash(keyToPassTogoodHash); // I think this has to do with the problem
makeKey(); // Call again to make a new key.
}
}
// Primary function to create our desired file!
void mainFunction(string fileName, int n) {
makeKey();
makeFile(fileName, n);
}
// Hash Table for Part 2
struct Node {
int key;
string value;
Node* next;
};
const int hashTableSize = 10;
Node* hashTable[hashTableSize];
// "goodHash" function for Part 2
void goodHash(string key) {
int x = 0;
int y;
int keyConvertedToNumber = 0;
// For-loop to produce a numeric value based on the alphabetic key,
// which is then hashed into hashTable using the hash function
// declared below the loop (hashFunction).
for (y = 0; y < 8; y++) {
if (key[y] == 'A' || 'B' || 'C')
x = 0;
if (key[y] == 'D' || 'E' || 'F')
x = 1;
if (key[y] == 'G' || 'H' || 'I')
x = 2;
if (key[y] == 'J' || 'K' || 'L')
x = 3;
if (key[y] == 'M' || 'N' || 'O')
x = 4;
if (key[y] == 'P' || 'Q' || 'R')
x = 5;
if (key[y] == 'S' || 'T')
x = 6;
if (key[y] == 'U' || 'V')
x = 7;
if (key[y] == 'W' || 'X')
x = 8;
if (key[y] == 'Y' || 'Z')
x = 9;
keyConvertedToNumber = x + keyConvertedToNumber;
}
int hashFunction = keyConvertedToNumber % hashTableSize;
Node *temp;
temp = new Node;
temp->value = key;
temp->next = hashTable[hashFunction];
hashTable[hashFunction] = temp;
}
// First two lines are for Part 1, to call the functions key to Part 1.
int main() {
srand ( time(NULL) ); // To make sure our randomization works.
mainFunction("sandwich.txt", 5); // To test program
cin.get();
return 0;
}
I realize my code is cumbersome in some sections, but I'm a noob at C++ and don't know much to do it better.
I'm guessing another way I could do it is to AFTER writing the alphabetical keys to the file, read them from the file and hash each key as I do that, but I wouldn't know how to go about coding that.

Answer 1

C++ expected everything to be declared in order, so that nothing's used before it's declared.
If you need to refer to a function higher in the file than where it's defined, you need to have a function prototype near the top of the file that declares the function. (Writing prototypes for all functions is a standard practice as a result of this.)
Near the top of the file (after the #includes) simply add
void goodHash(string key);
Definitions
Function declaration: something that declares the name of the function and the types the function takes.
Function definition: something that specifies the actual code of the function.

Answer 2

if you insert
void goodHash(string key);
in the line under "using namespace..." it will work

Answer 3

The issue is that you have to forward declare goodHash or define goodHash before makeFile if you want to use goodHash in makeFile. Otherwise, when the compile is in makeFile, it sees the token goodHash and hasn't found out what it means, which is why you are getting the compile-time error.
EDIT: Here is a good resource on forward declarations

Answer 4

you forgot the function prototype just add this in the top:
void goodHash(string key);
and btw your makeKey() is too long
you can try this instead:
string makeKey() {
int k;
string key = "";
for (k = 0; k < 8; k++) {
int keyNumber = (rand() % 25);
char app[2];
app[0] = keyNumber + 'A';
app[1] = 0;
key.append(app);
}
return key;
}