Q: But I heard that char a[] was identical to char *a.
A: Not at all. (What you heard has to do with formal parameters to functions; see question 6.4.) Arrays are not pointers, though they are closely related (see question 6.3) and can be used similarly (see questions 4.1, 6.8, 6.10, and 6.14).
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It is useful to realize that a reference like x[3] generates different code depending on whether x is an array or a pointer. Given the declarations above, when the compiler sees the expression a[3], it emits code to start at the location ``a'', move three past it, and fetch the character there. When it sees the expression p[3], it emits code to start at the location ``p'', fetch the pointer value there, add three to the pointer, and finally fetch the character pointed to. In other words, a[3] is three places past (the start of) the object named a, while p[3] is three places past the object pointed to by p. In the example above, both a[3] and p[3] happen to be the character 'l', but the compiler gets there differently. (The essential difference is that the values of an array like a and a pointer like p are computed differently whenever they appear in expressions, whether or not they are being subscripted, as explained further in question 6.3.) See also question 1.32.
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