Are grasshoppers, locusts and cicadas all the same thing?

Answer 1

No. Grasshoppers and locusts are similar, but locusts are generally larger than grasshoppers. Both can destroy crops. Cicadas, on the other hand, are more beetle-like. They are also the bugs you hear hissing in the trees during late summer.

Answer 2

No.
Grasshoppers are herbivorous insects of the suborder Caelifera in the order Orthoptera. To distinguish them from bush crickets or katydids, they are sometimes referred to as short-horned grasshoppers. Species that change colour and behaviour at high population densities are called locusts.

A cicada is any of several insects of the order Hemiptera, suborder Auchenorrhyncha, in the superfamily Cicadoidea, with small eyes wide apart on the head and transparent, well-veined wings. Cicadas live in temperate to tropical climates where they are one of the most widely recognized of all insects, largely due to their large size and remarkable (and often inescapable) acoustic talents. Cicadas are sometimes called "locusts", although they are unrelated to true locusts, which are a kind of grasshopper. Cicadas are related to leafhoppers and spittlebugs.