#!/usr/bin/env bash

num_students=$1
declare -a students

if [ $# -ne 1 ]; then
    echo "Error: expect 1 argument only!"
    exit 1
fi

for ((i = 0; i < num_students; i++)); do
    read -p "Student Name #$((i + 1)): " name
    read -p "Student Grade #$((i + 1)): " grade
    students+=("$name $grade")

    if [ $(expr "$grade" \> 100) -eq 1 ] || ! [[ "$grade" =~ ^[0-9]+$ ]]; then
        echo "Error: The grade '$grade' is not a valid input. Only numerical grades between 0 and 100 are accepted."
        exit 1
    fi
done

for student in "${students[@]}"; do
    name=$(echo $student | awk '{print $1}')
    grade=$(echo $student | awk '{print $2}')
    if [ "$grade" -ge 90 ]; then
        echo "$name: You did an excellent job!"
    elif [ "$grade" -ge 70 ]; then
        echo "$name: You did a good job!"
    elif [ "$grade" -ge 50 ]; then
        echo "$name: You need a bit more effort!"
    else
        echo "$name: You had a poor performance!"
    fi
done