Bits and bytes

A computer stores everything (numbers, text, pictures, programs) as bits: tiny switches that are either 0 or 1. Eight bits make a byte, the smallest piece of memory with its own address. With n bits you can write 2ⁿ different patterns: 8 bits give 256, 32 bits about 4.3 billion.

How big is each type?

#include <stdio.h>

int main(void) {
    printf("char      %zu byte\n", sizeof(char));
    printf("short     %zu bytes\n", sizeof(short));
    printf("int       %zu bytes\n", sizeof(int));
    printf("long long %zu bytes\n", sizeof(long long));
    printf("double    %zu bytes\n", sizeof(double));
    printf("int *     %zu bytes\n", sizeof(int *));
    int marks[10];
    printf("int[10]   %zu bytes\n", sizeof marks);
    return 0;
}

sizeof tells you how many bytes a type takes. On the computers StepVioz models (64-bit Linux, as on most servers and laptops):

Seeing the bits

#include <stdio.h>

int main(void) {
    int n = 13;
    printf("%d in binary: ", n);
    for (int i = 7; i >= 0; i--) {
        int bit = (n >> i) & 1;
        printf("%d", bit);
    }
    printf("\n");
    return 0;
}

This program prints the 8 bits of a number, from the highest to the lowest. (n >> i) & 1 moves bit i to the end and keeps only it. 13 is 00001101: 8 + 4 + 1. Each bit position is worth twice the one to its right: 128, 64, 32, 16, 8, 4, 2, 1.

Mark lesson complete