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Foundations: how computers work

Bits and bytes, binary and hex, negative numbers, bitwise tricks, floating point, text, memory and how a program runs, explored in C.

• Online C compiler
• C code visualizer
• Foundations exercises with solutions

1. 1

   Bits and bytes

   Everything in a computer is stored as bits; eight bits make a byte, and every type has a size in bytes.

2. 2

   Number systems: binary, octal and hexadecimal

   The same number written in base 10, base 2, base 8 and base 16, and how to convert between them.

3. 3

   Negative numbers and overflow

   Two's complement stores negative numbers; unsigned numbers wrap around; signed overflow is a bug.

4. 4

   Bitwise operations

   AND, OR, XOR, NOT and shifts work on single bits: test, set and clear flags, and multiply by powers of two.

5. 5

   Floating-point numbers

   Why 0.1 + 0.2 is not exactly 0.3: doubles store binary fractions with about 15 significant digits.

6. 6

   Characters and text

   A character is a small number: ASCII codes, letter arithmetic, and how UTF-8 stores Bangla and emoji in several bytes.

7. 7

   Memory: addresses, the stack and the heap

   Memory is a long row of numbered bytes; where globals, locals and malloc blocks live, and the byte order of an int.

8. 8

   How a program runs

   From source code to machine instructions: compiling, linking, the CPU's fetch-decode-execute loop, and the call stack.