Misc Objective-C Notes

Stuff to remember

Remember the Ternary Operator

int minutesPerPound = isBoneless ? 10 : 15;
In this case, if true then assign 10, else assign 15.
REMEMBER THIS

Global Variables and Static Variables

• Global variables are defined outside of any functions like so:

#include <stdio.h>
#include <stdlib.h>

// Declare a global variable here
float thisIsGlobal;

void nextFunctionHere {
    return 0;
}

• Static variables are also defined outside any functions, but are only available within a given file, to limit scope somewhat.

#include <stdio.h>
#include <stdlib.h>

// Declare a static variable here
static float thisIsAStaticVariable;

void nextFunctionHere {
    return 0;
}

Looping Notes

• break stops execution in the middle of the loop
• continue skips to the next iteration of the loop (INTERESTING)
  • see page 59 of BNR Objective C Programming 2nd Edition

Example of passing arguments via "reference"

#include <stdio.h>
#include <math.h>

void metersToFeetAndInches(double meters, double *ftPtr, double *inPtr) {

    *inPtr = modf(meters * 3.281, ftPtr) * 12.0;

}

int main(int argc, const char * argv[]) {

    double meters = 20.0;
    double feet, inches;

    metersToFeetAndInches(meters, &feet, &inches);
    printf("%.1f meters is equal to %.0f feet and %.2f inches. \n", meters, feet, inches);

    return 0;
}

• See page 72-73 in BNR Objective C Programming 2nd Edition
• See page 74 to read about dereferencing NULL IMPORTANT

Structs in C

• Used when you need a variable to hold many pieces of data
  • Each "chunk" of data is known as a member of the struct

#include <stdio.h>

typedef struct {
    float heightInMeters;
    int weightInKilos;
} Person;

float bodyMassIndex(Person p) {
    return p.weightInKilos / (p.heightInMeters * p.heightInMeters);
}

int main(int argc, const char * argv[]) {

    Person mikey;
    mikey.heightInMeters = 1.7;
    mikey.weightInKilos = 96;

    Person aaron;
    aaron.heightInMeters = 1.97;
    aaron.weightInKilos = 84;

    printf("mikey is %.2f meters tall\n", mikey.heightInMeters);
    printf("mikey weights %d kilograms \n", mikey.weightInKilos);
    printf("mikey has a BMI of %.2f\n", bodyMassIndex(mikey));
    printf("aaron is %.2f meters tall\n",aaron.heightInMeters);
    printf("aaron weighs %d kilograms\n", aaron.weightInKilos);
    printf("aaron has a BMI of %.2f\n", bodyMassIndex(aaron));

    return 0;
}

This is an example of using defining a struct with a typedef as per page 76 in BNR 2nd edition