// ---- @interface ----
  @interface Fraction : NSObject {  // inherit from NSObject
      int numerator;
      int denominator;
  }
  - (void)print;
  - (void)setNumerator:(int)n;
  - (void)setDenominator:(int)d;
  @end

  // ---- @implementation ----
  @implementation Fraction   // you can optionally specify :NSObject after Fraction
  - (void)print { NSLog(@"%i/%i", numerator, denominator); }
  - (void)setNumerator:(int)n { numerator = n; }
  - (void)setDenominator:(int)d { denominator = d; }
  @end

@import <limits.h>
  // ...
  NSLog(@"CHAR_MIN:   %c",   CHAR_MIN);
  NSLog(@"CHAR_MAX:   %c",   CHAR_MAX);
  NSLog(@"SHRT_MIN:   %hi",  SHRT_MIN);    // signed short int
  NSLog(@"SHRT_MAX:   %hi",  SHRT_MAX);
  NSLog(@"INT_MIN:    %i",   INT_MIN);
  NSLog(@"INT_MAX:    %i",   INT_MAX);
  NSLog(@"LONG_MIN:   %li",  LONG_MIN);    // signed long int
  NSLog(@"LONG_MAX:   %li",  LONG_MAX);
  NSLog(@"ULONG_MIN not defined, it's always zero: %lu", 0);  
  NSLog(@"ULONG_MAX:  %lu",  ULONG_MAX);   // unsigned long int
  NSLog(@"LLONG_MIN:  %lli", LLONG_MIN);   // signed long long int
  NSLog(@"LLONG_MAX:  %lli", LLONG_MAX);
  NSLog(@"ULLONG_MIN not defined, it's always zero: %llu", 0);  
  NSLog(@"ULLONG_MAX: %llu", ULLONG_MAX);  // unsigned long long int

char (‘a’, ‘\n’): %c
short int: %hi, %hx, %ho
unsigned short int: %hu, %hx, %ho
int (17, -99, 0xFFAE, 0878): %i, %x, %o
unsigned int (17u, 101U, OXFFu): %u, %x, %o
long int (17L, -2998, OxffffL): %li, %lx, %lo
unsigned long int (17UL, -100ul, OxffeeUL): %li, %lx, %lo
long long int (0xe5e5e5e5LL, 500ll): %lli, %llx, %llo
unsigned long long int (17ull, oxffefULL): %llu, %llx, %llo
float (12.3f, 3.1e-5f, 0×1.5p10, 0×1P-1): %f, %e, %g, %a
double (12.34, 3.1e-5, 0×.1p3): %f, %e, %g, %a
long double (12.34l, 3.1e-5l): %Lf, %Le, %Lg
id (nil): %p