Array Basics

Declaration and indexing

int scores[5];              // 5 ints, UNINITIALIZED (indeterminate values)
int primes[4] = {2, 3, 5, 7};
int first = primes[0];      // 2 — indexing starts at 0
int last  = primes[3];      // 7 — index size-1

• Elements live contiguously in memory: primes[i] sits at "start + i * sizeof(int)".
• The size is part of the type — fixed at compile time (dynamic sizing is module 13).
• The compiler will not stop you from reading primes[9] — that is undefined behavior. Out-of-bounds access is THE classic C bug.

Initialization rules

int a[4] = {1, 2};          // {1, 2, 0, 0} — rest zero-filled
int b[]  = {1, 2, 3};       // size deduced: 3
int c[4] = {0};             // all zeros

Any initializer list (even {0}) gives defined values; no list at all leaves the contents indeterminate — reading them is a bug.

No length operator

C arrays do not know their own length. Passing them to functions loses the size — you pass it separately (module 12). For now: keep a constant.

#define N 5
int a[N];
for (int i = 0; i < N; i++) { /* ... */ }