Vigener cipher, looping the key - c

Question

I would like to ask your help about my program. It will be a vigenere-cipher solution, but I have to encrypt it from a file.
My problem is that I can't loop my keyword for the message length.
There are the tasks
Ask the message you want to translate,maximum 255 character
I have to transform the message to unaccented,upper case and without spaces
Than print it to the screen.
Ask the key, maximum five character and the same transformation.
I have to loop the key for the lenght of the message. than print it to the screen. Now that's what I can't do.
Can somebody please help me in it?
#include <stdio.h>
#include <ctype.h>
#define MAX 256
#define KMAX 6
void mess(void){
char message[MAX];
int j,i,k=0;
char big[]={"ÁÉÍÓÖŐÚÜŰ"}, small[]={"áéíóöőúüű"}, english[]={"aeiooouuu"};
printf("Please give the message you want to enrypt! Maximum %d character: ",MAX-1); // 1.
fgets(message,MAX,stdin); // 2.
for(i=0;message[i];i++){
j=0;
while(small[j] && (message[i]!=small[j] && message[i]!=big[j])){
j++;
}
if(small[j]){
message[i]=english[j];
}
if(isalpha(message[i])){
message[k]=toupper(message[i]); k++;
}
}
message[k]='\0';
printf("\nThe clean message is: %s\n\n",message);
}
void keyword(void){ // 3.
char key[KMAX];
int j,i,k=0;
char big[]={"ÁÉÍÓÖŐÚÜŰ"}, small[]={"áéíóöőúüű"}, english[]={"aeiooouuu"};
printf("Please give the key!Maximum %d character\n",KMAX-1);
fgets(key,KMAX,stdin);
for(i=0;key[i];i++){
j=0;
while(small[j] && (key[i]!=small[j] && key[i]!=big[j])){
j++;
}
if(small[j]){
key[i]=english[j];
}
if(isalpha(key[i])){
key[k]=toupper(key[i]); k++;
}
}
key[k]='\0';
printf("\nThe clean key is: %s\n\n",key);
}
void loop() //4.
{
}
int main(void){ // main
system("CHCP 1250");
system("CLS");
mess();
keyword();
loop();
return 0;
}