Arrays and Indexes

An array stores an ordered group of values of the same type. Every element is accessed by index, and the array length is fixed when it is created.

Creating arrays

Use an array initializer when the values are known. int counts[4] = {0} creates four zero-initialized slots. The element type comes before the variable name, and brackets mean “a group of this type.”

int scores[] = {88, 91, 76, 95, 83};
int counts[4] = {0};
counts[0] = 12;
counts[1] = 9;

Initializing an int array with {0} sets every element to 0; an uninitialized local array does not receive automatic default values. The slot count is decided when the array is created.

Accessing array elements

Array indexes start at 0, so the first element is scores[0]. An array of length 5 has indexes 0 through 4. Accessing scores[5] does not throw automatically; it causes undefined behavior.

int scores[] = {88, 91, 76, 95, 83};
printf("%d\n", scores[0]); // 88
printf("%d\n", scores[4]); // 83
scores[2] = 80;
printf("%d\n", scores[2]); // 80

Array length and loops

Built-in arrays have no length field. This array has five elements, so the example directly uses score_count = 5; the last valid index is score_count - 1.

int score_count = 5;

for (int i = 0; i < score_count; i++) {
    printf("scores[%d] = %d\n", i, scores[i]);
}

for (int i = 0; i < score_count; i++) {
    printf("%d\n", scores[i]);
}

Fixed length and common operations

You can read or rewrite existing elements and use a loop to find a value. None of these actions adds or removes slots.

int values[] = {4, 0, 7, 0, 2, 9};
int count = 6;
values[2] = 5;

for (int i = 0; i < count; i++) {
    if (values[i] == 0) {
        printf("Found 0 at index %d\n", i);
    }
}