Hill cipher in C?

Question

Encryption

There is a code that encrypts a string of 3 letters. Help change it so that there is no limit on the number of letters per line.

#include<iostream>
#include<math.h>
#include<stdio.h>
 
using namespace std;
 
float encrypt[3][1], decrypt[3][1], a[3][3], b[3][3], mes[3][1], c[3][3];
 
void encryption();    //encrypts the message
void decryption();    //decrypts the message
void getKeyMessage();    //gets key and message from user
void inverse();        //finds inverse of key matrix
 
int main() {
    getKeyMessage();
    encryption();
    decryption();
    system ("pause");
}
 
void encryption() {
    int i, j, k;
    
    for(i = 0; i < 3; i++)
        for(j = 0; j < 1; j++)
            for(k = 0; k < 3; k++)
                encrypt[i][j] = encrypt[i][j] + a[i][k] * mes[k][j];
    
    cout<<"\nEncrypted string is: ";
    for(i = 0; i < 3; i++)
        cout<<(char)(fmod(encrypt[i][0], 26) + 97);
}
 
void decryption() {
    int i, j, k;
    
    inverse();
    
    for(i = 0; i < 3; i++)
        for(j = 0; j < 1; j++)
            for(k = 0; k < 3; k++)
                decrypt[i][j] = decrypt[i][j] + b[i][k] * encrypt[k][j];
    
    cout<<"\nDecrypted string is: ";
    for(i = 0; i < 3; i++)
        cout<<(char)(fmod(decrypt[i][0], 26) + 97);
    
    cout<<"\n";
}
 
void getKeyMessage() {
    int i, j;
    char msg[4];
 
    cout<<"Enter 3x3 matrix for key (It should be inversible):\n";
    
    for(i = 0; i < 3; i++)
        for(j = 0; j < 3; j++) {
            scanf("%f", &a[i][j]);
            c[i][j] = a[i][j];
        }
    
    cout<<"\nEnter a 3 letter string: ";
    cin>>msg;
    
    for(i = 0; i < 3; i++)
       mes[i][0] = msg[i]-97;
}
 
void inverse() {
    int i, j, k;
    float p, q;
    
    for(i = 0; i < 3; i++)
        for(j = 0; j < 3; j++) {
            if(i == j)
                b[i][j]=1;
            else
                b[i][j]=0;
        }
        
    for(k = 0; k < 3; k++) {
        for(i = 0; i < 3; i++) {
            p = c[i][k];
            q = c[k][k];
                
            for(j = 0; j < 3; j++) {
                if(i != k) {
                    c[i][j] = c[i][j]*q - p*c[k][j];
                    b[i][j] = b[i][j]*q - p*b[k][j];
                }
            }
        }
    }
    
    for(i = 0; i < 3; i++)
        for(j = 0; j < 3; j++)
            b[i][j] = b[i][j] / c[i][i];
    
    cout<<"\n\nInverse Matrix is:\n";
    for(i = 0; i < 3; i++) {
        for(j = 0; j < 3; j++)
            cout<<b[i][j]<<" ";
        
        cout<<"\n";
    }
}