How an enum is convert when it is out of index in C

Question

In C++, I see

#include <iostream>

typedef enum {
    NORMAL = 0,
    EXTENDED
} CyclicPrefixType_t;

void func (CyclicPrefixType_t x) {
    if(x < NORMAL){
        printf ("lower\n");
    }else{
        printf ("higher\n");
    }
}

int main (void) {
    //MUST CAST OR WE GET ERROR
    CyclicPrefixType_t cpType = CyclicPrefixType_t(NORMAL - 1);

    func (cpType);
    return 0;
}

Run the code on C++

Expected: lower > It is OK

But in C,

#include <stdio.h>

typedef enum {
    NORMAL = 0,
    EXTENDED
} CyclicPrefixType_t;

void func (CyclicPrefixType_t x) {
    if(x < NORMAL){
        printf ("lower\n");
    }else{
        printf ("higher\n");
    }
}

int main (void) {
    //NO NEED TO CAST
    CyclicPrefixType_t cpType = (NORMAL - 1);

    func (cpType);
    return 0;
}

Run the code on C

Actually Result: Higher > It is NOT OK

In this case, (-1) is automatically cast to another value. Anyone can tell me which value is here and how it is converted to Because if you print it(%d), It will still (-1)