[Adult Learning Log] C Language - Week 3 Review

○ Key Takeaways from Week 3

• Learned how to use sizeof to find out the memory size occupied by a variable or data type.
• Understood the concepts of variables and constants, and the classification, size, and range of data types.
• Learned about unsigned, signed type specifiers and how to use suffixes to specify data types for integer constants.
• Studied symbolic constants and the differences between constants and variables.
• Learned the concept of Underflow, which is the opposite of Overflow.

○ Review Highlights

• Reviewed the concept of Overflow and the importance of selecting appropriate data types.
• Revisited how negative numbers are represented in computers using Two's Complement.
• Reviewed fixed-point vs. floating-point number representations.
• Refreshed understanding of ASCII codes.

○ Data Types and Sizes: (1) Integer Types

• short : 16-bit (2 bytes) → Range: -2^15 ~ 2^15 - 1
• int : 32-bit (4 bytes) → Range: -2^31 ~ 2^31 - 1
• long : 32-bit (4 bytes) → Range: -2^31 ~ 2^31 - 1
• long long : 64-bit (8 bytes) → Range: -2^63 ~ 2^63 - 1

Why are there so many integer types in C?

• Allows programmers to choose appropriate types based on use-case.
• Increasing the bit size extends the range but consumes more memory.

○ Signed vs Unsigned

• unsigned: Represents only non-negative values. No sign bit required.
  
  → For 32 bits: 0 ~ 2^32 - 1

• signed: Includes both positive and negative values (usually default as int).
  
  → With 1 bit for sign, 31 bits remain for value: -2^31 ~ 2^31 - 1

○ Integer Constant Suffixes

• u or U → unsigned (e.g., 123u)
• l or L → long (e.g., 123L)
• ul or UL → unsigned long (e.g., 123UL)

○ Overflow

• Occurs when data exceeds the size limits of its data type.
• Can lead to incorrect results or system behavior.
• Happens when the sum requires more bits than available.
• If the sign bit in the result differs from operands, overflow occurs.
• Always choose data types with sufficient size to prevent overflow.

○ Symbolic Constants

• Constants expressed using symbols (e.g., #define) for readability and maintainability.
• Changing a value in one place instead of multiple occurrences makes code maintenance easier.

#define EXCHANGE_RATE 1120    // preferred
// #define EXCHANGE_RATE = 1120; → incorrect

Symbolic Constant vs Variable

• #define is a preprocessor directive and is replaced before compilation.
• It does not occupy memory or have a data type.
• Variables are stored in memory and can be changed at runtime.
• Think of symbolic constants as constant variables that don’t exist in memory.

○ Data Types and Sizes: (2) Floating Point Types

• float: 32-bit (4 bytes) → Single precision, ~7 decimal digits
• double: 64-bit (8 bytes) → Double precision, ~15~16 decimal digits
• long double: 64-bit+ → Extended precision (compiler-dependent)

Fixed vs Floating Point

• Fixed-point: Simple but limited for large numbers
• Floating-point: Used in science/engineering for representing very large/small numbers

Floating-point Overflow & Underflow

• Overflow: Too large to represent → often shows inf
• Underflow: Too small to represent

Why decimal for float range but binary for int?

• Integers stored in binary → binary ranges (2^n) are precise and meaningful.
• Floats care about how many decimal digits can be represented accurately, so decimal notation is more informative.

○ Data Types and Sizes: (3) Character Type

• char type stores characters using ASCII codes.

Control Characters

• Non-printable characters used for control:
  • \0 → null terminator (marks end of string)
  • \a → bell (beep sound)
  • \b → backspace
  • \t → horizontal tab
  • \n → newline
  • \v → vertical tab
  • \f → form feed
  • \r → carriage return
  • \", \', \\ → literal quote or backslash

\0 Null Terminator

• Marks end of a string in memory.
• Strings in C are arrays of characters; they don't store length separately.
• So \0 acts like a period to signify end of the string.

○ Practice Activities

Practice 1: sizeof

• Use sizeof to display memory size for various data types and variables.

Practice 2: Currency Converter

• Input USD amount → output converted KRW amount.
• Use Symbolic Constant for exchange rate.

Practice 3: ASCII & Char Practice

• Print numeric and character values using ASCII codes.