Testing length of inputed message with old message - c

Question

I'm working on a program that asks me to enter a new message and replacing the old one, but I have to test if the message is longer than the last one. I would like to get answer that is similar to my program because this is a lesson I'm learning right now. It asks me to input size of new char, but when I test it, it takes my set size for testing.
#include <stdio.h>
#include <stdlib.h>
void editedMessage(char* nmessage, int size){
char newMessage[];
printf("Enter a new message!\n");
gets_s(newMessage, sizeof(newMessage));
if (size > sizeof(newMessage)){
for (int i = 0; i < sizeof(newMessage); i++){
nmessage[i] = newMessage[i];
}
}
else {
printf("New message is too long.\n\n");
}
}
void main(){
char message[] = "This is some message!";
printf("Old message\n%s\n\n", message);
editedMessage(message, sizeof(message));
printf("New message\n\n%s\n\n", message);
}
EDIT: I edited next code but now says 'stack around the variable 'message' was corrupted'
char newMessage[256];
printf("Enter a new message!\n");
gets_s(newMessage, sizeof(newMessage));
int len = strlen(newMessage);
if (size > len){
for (int i = 0; i < sizeof(newMessage); i++){
nmessage[i] = newMessage[i];
}
}

Answer 1

I changed the return type of editedMessage to char* and cut down it arguments.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_LENGTH 1000
char* editedMessage(char* oldMessage){
char newMessage[MAX_LENGTH];
printf("Enter a new message : ");
fgets(newMessage,MAX_LENGTH,stdin);
if (strlen(newMessage)<= strlen(oldMessage)){
strcpy(oldMessage,newMessage);
}
else {
printf("New message is too long.\n\n");
}
return oldMessage; // In fact the value of oldMessage should have been changed if the new message is shorter in length
}
void main(){
char message[MAX_LENGTH] = "This is some message!";
printf("Old message : %s\n", message);
editedMessage(message);
/* Since we are dealing with pointers, note that I am not catching any
* return values here. In essence any changes made to message in the
* editedMessage function is automatically effective in the main
* function.
*/
printf("New message :%s\n", message);
}