4.1.1 Array Initialization

Although it is not possible to assign to all elements of an array at once using an assignment expression, it is possible to initialize some or all elements of an array when the array is defined. The syntax looks like this:

	int a[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};

The list of values, enclosed in braces {}, separated by commas, provides the initial values for successive elements of the array.

(Under older, pre-ANSI C compilers, you could not always supply initializers for ``local'' arrays inside functions; you could only initialize ``global'' arrays, those outside of any function. Those compilers are now rare, so you shouldn't have to worry about this distinction any more. We'll talk more about local and global variables later in this chapter.)

If there are fewer initializers than elements in the array, the remaining elements are automatically initialized to 0. For example,

	int a[10] = {0, 1, 2, 3, 4, 5, 6};

would initialize a[7], a[8], and a[9] to 0. When an array definition includes an initializer, the array dimension may be omitted, and the compiler will infer the dimension from the number of initializers. For example,

	int b[] = {10, 11, 12, 13, 14};

would declare, define, and initialize an array b of 5 elements (i.e. just as if you'd typed int b[5]). Only the dimension is omitted; the brackets [] remain to indicate that b is in fact an array.

In the case of arrays of char, the initializer may be a string constant:

	char s1[7] = "Hello,";
	char s2[10] = "there,";
	char s3[] = "world!";

As before, if the dimension is omitted, it is inferred from the size of the string initializer. (We haven't covered strings in detail yet--we'll do so in chapter 8--but it turns out that all strings in C are terminated by a special character with the value 0. Therefore, the array s3 will be of size 7, and the explicitly-sized s1 does need to be of size at least 7. For s2, the last 4 characters in the array will all end up being this zero-value character.)

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