Arrays and strings in C

Contiguous memory, the missing bounds check, and why a C string needs its null terminator.

12 min read · Lesson 6 of 6 · Pro

An array is one block of memory

#include <stdio.h>

int main(void)
{
    int marks[5] = {90, 75, 88, 60, 100};
    int i, total = 0;

    for (i = 0; i < 5; i++)
        total += marks[i];

    printf("Total %d, average %.2f\n", total, total / 5.0);
    return 0;
}

int marks[5] reserves 5 x 4 = 20 bytes, side by side, no gaps. marks[3] means "go to the start of the array, skip 3 x 4 = 12 bytes, read 4 bytes". That single multiplication is why array access is fast, and why the index starts at 0 — the first element needs no skipping.

Prove it to yourself:

#include <stdio.h>

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