Write a C$++$ program that prompts the user to enter the name, surname, Test $1$ mark, and Test $2$ mark of a student. The program should then use three functions: calculateAverage, gradeAverage, and printDetails as follows:

calculateAverage: This function should take two integer parameters representing the Test $1$ mark and Test $2$ mark and return the average of the two marks as a double.

gradeAverage: This function should take the average mark as a parameter and return a string indicating whether the student has passed or failed. If the average mark is greater than or equal to $50,$ the function should return "Passed"; otherwise, it should return "Failed".

printDetails: This function should take the student's name, surname, Test $1$ mark, Test $2$ mark, average mark, and grade as parameters and display these details to the console. This function is a void function.