¿Por qué debemos poner un signo de pregunta antes de la palabra y la palabra de exclamación
Vienen tus padres a comer mañana por la noche
Vienen tus padres a comer mañana por la noche?
Look how similar the two sentences above are. The first one is saying that "Your parents are coming...", while the second one is asking "Are your parents...?" English reverses the order from "Your parents are" to "Are your parents" at the very beginning of the sentence, which is the signal you need to start reading it as a question. Since in Spanish this inversion is not compulsory (although it can be used), without clues we do not know how to read the sentences... unless we go to the end of the sentence to check whether there is an interrogation mark at the end or not. For this, we signal the start of a question with "¿". Regarding "¡", it is a very useful sign, because we could start a sentence with a normal tone, and at any point, raise it to make it an exclamation. In English you have to capitalize the whole thing in these cases; we simply use "¡" when we intend to raise the tone.
I think that you received your answer in the chastisement given below your question. It is proper punctuation. What more reason do you need?
You can also have ¿! or ¡? with exclamatory interrogatives ¡Qué?