How to Initialize All Elements of a C Array to a Specific Non-Zero Value?

Initializing Elements of an Array to a Default Value in C

The question arises from an array initialization in C using the syntax:

int array[100] = {-1};

This initialization sets the first element to -1 and leaves the remaining elements at 0, which isn't the desired behavior. To address this, the following points need consideration:

Syntax Interpretation

The syntax int array[100] = {-1}; essentially says, "set the first element to -1, and the rest to 0." When elements are omitted in an array declaration, they are automatically initialized to 0 by default.

Setting All Elements to a Non-Zero Value

To initialize all elements to a non-zero value like -1, one cannot rely solely on the default omitted value initialization. Instead, the following approaches can be used:

1. std::fill_n: Using the std::fill_n function from the library:

std::fill_n(array, 100, -1);

2. Looping: In standard C , creating a loop to assign values to each element would be necessary:

for (int i = 0; i < 100; i++) {
  array[i] = -1;
}

Speed Comparison

The speed of default initialization compared to a loop is not significantly different. Both approaches initialize elements sequentially, so the time complexity remains the same. However, using std::fill_n can save a few instructions compared to a manual loop, making it slightly faster in most cases.

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