Write a function called num$\_$days$\_$big$\_$percent$\_$chg that has two inputs: a $1-$D array that contains the values of a stock index and a number that is a percent. The function calculates and returns the total number of trading days where the magnitude of the percent change $($up or down$)$ in the stock index since the previous day is greater than the value of the percent input into the function. Do not use loops or loop$-$like structures like list comprehensions.