function areaOfCircle(radius) {
    this.radius = radius;
    this.area = function() {
            return Math.PI * (radius * radius);
        }
    }

/* calling the function passing in a number for the radius */
areaOfCircle(2);
if (radius != null || radius != undefined){
    console.log('\nThe area of a circle is: ' + area() +
    '\nAlso the area of said circle rounded to two decimal points is: ' + area().toFixed(2));
}
else if (radius == null || radius == undefined) {
    console.log('\nError: null or undefined variable in the place of radius variable.\n');
}

/* calling the function passing in null for the radius */
areaOfCircle(null);
if (radius != null || radius != undefined){
    console.log('\nThe area of a circle is: ' + area() +
    '\nAlso the area of said circle rounded to two decimal points is: ' + area().toFixed(2));
}
else if (radius == null || radius == undefined) {
    console.log('\nError: null or undefined variable in the place of radius variable.\n');
}