Write a program to compute the evaluation of a user$-$defined cubic polynomial at

x $=2.$ Recall that a cubic polynomial is any function f of the form

f $($x$)=$ ax$3+$ bx$2+$ cx $+$ d$,$

where a$,$ b$,$ c and d are real numbers, which the user will specify. The evaluation of f

at x $=2$ is therefore given by

f $(2)=8$a $+4$b $+2$c $+$ d$.$

You should first ask the user to specify a polynomial by writing a string in the following

format:

f$($x$)=[$number$]*$x$^3+[$number$]*$x$^2+[$number$]*$x$+[$number$].$ use stod $($string to double$)$