How can I fix my compiling error on line 12?

[Kernmaster22]

Hi, I need help with my program. How can I fix my compiler error on line 12 of me code? It's not working for some reason. May I have feedback please?
This is the problem:

Your country is at war and your enemies are using a secret code to communicate
with each other. You have managed to intercept a message that
reads as follows:

:mmZ\dxZmx]Zpgy

Write a program that decrypts the intercepted message. You only know
that the key used is a number between 1 and 100. Your program should
try to decode the message using all possible keys between 1 and 100.
When you try the valid key, the message will make sense. For all other
keys, the message will appear as gibberish.

#include <iostream>
#include <string>
#include <vector>

using namespace std;

void input(char message[100], int& key);
vector<char> encrypt(char message[100], int key);

int main()
{
    input(message[100], key);
    vector<char> encrypt(char message[100], key);

    return 0;
}

void input(char message[100], int& key)

{
    cout << "Please enter an encrypted message: \n";
    cin.getline(message,100);
}

vector<char> encrypt(char message[100], int key)

{
    int counter;
    char output[100];

    for(key = 1; key <= 100; key++)
    {
        for(counter = 0; message[counter]! = '\0' ; counter++)
        {
            if(message[counter] - key < 32)
                output[counter] = message[counter] - key - 32 + 127;
            else
                output[counter] = message[counter] - key;
        }

        cout << "Decrypted message using Key" << key << " : ";
        cout << output << endl;
    }

}

[divideby0]

 input(message[100], key);

the call here isn't right. you haven't declared any variables named input or key. declare a char array and an integer variable, and pass them as parameters to input.

char array[100] = { 0 };
int key;

input(array, key);

void input(char message[100], int& key)
{
cout << "Please enter an encrypted message: \n";
cin.getline(message,100);
}

the function doesn't appear to change key in any way. are you supposed to alter its value?