Check user input for errors in bash script

This should do:

#!/bin/bash
printf -v prompt '%s\n' "nhat and betah for each element" "TIPS: 4 REAL NUMBER for each element(eg, 1.0 0.0 1.0 .1)"
while read -p "$prompt" -a nbh; do
   ((${#nbh[@]}==4)) && break
   echo "Wrong!!"
done

(I've tried to render the script more acceptable regarding good practices).

Now you have a problem: how are you going to check that the user really inputs numbers? Let's pretend you have a function that can tell if a string is a valid representation of a number you accept. Let's call this function banana because it's a nice name. Then:

#!/bin/bash

banana() {
    # Like its name doesn't tell, this function
    # determines whether a string is a valid representation
    # of a number
    # ...
    # some wicked stuff here
    # ...
}

printf -v prompt '%s\n' "nhat and betah for each element" "TIPS: 4 REAL NUMBER for each element(eg, 1.0 0.0 1.0 .1)"
good=0
while ((!good)) && read -p "$prompt" -a nbh; do
    if ((${#nbh[@]}!=4)); then
        echo "Wrong!! you must give 4 numbers! (and I can count!)"
        continue
    fi
    for i in "${nbh[@]}"; do
        if ! banana "$i"; then
            echo "Your input \`$i' is not a valid number. It might be a valid banana, though. Check that with the local gorilla."
            continue 2
        fi
    done
    # If we're here, we passed all the tests. Yay!
    good=1
done

# At this point, you should check that we exited the loop because everything was
# valid, and not because `read` has an error (e.g., the user pressed Ctrl-D)
if ((!good)); then
    echo >&2 "There was an error reading your input. Maybe a banana jammed in the keyboard?"
    exit 1
fi

# Here you're safe: you have 4 entries that all are valid numbers. Yay.
echo "Bravo, you just won a banana!"

Now, for the function banana, you might want to use a regex (but then we'll have two problems, oh dear):

banana() {
    [[ $1 =~ ^-?([[:digit:]]*\.?[[:digit:]]+|[[:digit:]]+\.?[[:digit:]]*)$ ]]
}

Note that the scientific form is not supported here, so inputs like 1e-6 will not pass the test. If you need to also handle this, good luck, you're on your own!

You could also add an easter egg in your script: just after the while line, add:

[[ ${nbh[0],,} = gorilla ]] && { echo "banana"; continue; }
[[ ${nbh[0],,} = banana ]] && { echo "gorilla"; continue; }

Cheers!