lesson 2 c intro and lesson 3 storage

C language directives

#if, #ifdef, ifndef, endif, else, elif, include, define, undef, pragma, error, line

Compile with the -Wall flag!

WORKSHEET

int isPrime(int n) {
  int i;
  if(n < 2) return 0;
  for(i=2; i<n/2+1; i++) {
    if(n%i == 0) {
      return 0;
    }
  }
  return 1;
}

int sumPrimes(int x) {
  int total = 0;
  int i;
  for(i=2; i<=x; i++) {
    if(isPrime(i)) {
      total += i;
    }
  }
  return total;
}

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Lesson 3

C is a weakly typed language-- associates a type with every value, allows for implicit conversions between some types

Types only exist at the code level; machine level has no knowledge of types

A byte is the smallest addressable unit of memory-- 8 bits

Binary representation of data changes based on data type:
- unsigned (traditional)
- two's complement (signed)
- fixed/floating point

Hexadecimal used to represent bytes-- 0x00 to 0xFF
- string ex3: 65 78 33

Little endian systems (x86)-- MSB is later address: 33 78 65
Big endian (sun. ibm)-- MSB at earlier address: 65 78 33

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Bitwise Operators-- | & ^
|| != && are logical operators (byte level)

>> and << are bitwise shift
- Left shift: 67 << 5 = 01000011 << 5 = 01100000 = 96
- Logical right shift (unsigned)
- Arithmetic right shift (signed) -- pad with zeros if first is 0
- Arithmetic right shift (signed) -- pad with 1 if first is 1

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Overflow (when sizes are too small)-- it loops back around since there's only 4 bits / 0 to 15