Array type char[] is not assignable

You can't assign to an array, only copy to it.

Use strcpy instead, like

strcpy(word, "Jump");

TL;DR answer : An array name is not a modifiable lvalue. So, you cannot use the assignment operator (=) on that.

To copy the content into the array, you need to use strcpy() from string.h (char array) or memcpy() in general.

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Now, to elaborate the actual reason behind the error message, quoting C11, chapter §6.5.16, Assignment operators

assignment operator shall have a modifiable lvalue as its left operand.

and then, quoting chapter §6.3.2.1 from the same standard,

A modifiable lvalue is an lvalue that does not have array type, [....]

So, an array name is not a modifiable lvalue hence, you cannot assign anything to it. This is the reason behind the error message.