How to code function if nothing, or wrong input is entered to ask aqain for input + what is wrong. It is possible everything split in functions?

Question

#include <stdlib.h>
#include <stdio.h>

char
input(char emailInput[100])
{
    printf("Enter email:");             // if nothing or wrong email is input repeat//
    gets(emailInput);
}

char
checkInputEtDot(char emailInput[100])
{
    int i, checkET, checkDot;

    checkET = checkDot = 0;

    for (i = 0; emailInput[i] != '\0'; i++) {
        if (emailInput[i] == '@')       // if @ is not entered ask again + ask for @//
            checkET = i;
        if (emailInput[i] == '.')       // if . is not entered ask again + ask for .//
            checkDot = i;
    }

    if (checkET < 1)                    // seperate function for every validation//
        printf("you need @\n");         // function for "@"; if function OK continue//
    // if not ask again//
    if (checkET < 3)
        printf("you need at least 3 charachters before @\n");
    if (checkDot < 1)
        printf("you need .\n");

    if (checkET > 3 && (checkDot - checkET) > 3)
        printf("Email is OK");
    else
        printf("Email is NOT OK");

    printf("\n");
}

void
main()
{
    char emailInput[100], checkEmailInput;

    input(emailInput);
    checkInputEtDot(emailInput);
}

for example when input function is not ok, repeat, if ok than check function for "@", if ok function for "." than function for at least 3 characters before "@", if ok, function for 3 characters after "@", if ok , at least 2 characters after ".".

for now that all working, but i need functions so i can upgrade validation process with special charachters.