Exercise $4\mathrm{.}4$ In this exercise you will practice using selection statements with

functions

a$.$ Define a function and a prototype called validate that has one parameter, an

int. If the int is $0$ the function should print an error message and terminate. If

the parameter is non$-$zero, multiply the value by $2$ and print the result.

b$.$ Define a main function that calls your function $3$ times with the following arguments: $0,3,-2$