typedef struct pet Pet;

struct pet {
    char name[MAX_LEN];
    char breed[MAX_LEN];
    int age;
};

int main(void){
    Pet myPet;
    strcpy(myPet.name,"Boris"); 
    strcpy(myPet.breed,"dog"); 
    myPet.age = 7;
    
    etc...

typedef struct date Date;

struct date {
    int day;
    int month;
    int year;
};

typedef struct pet Pet;

struct pet {
    char name[MAX_LEN];
    char breed[MAX_LEN];
    Date dateOfBirth;
};

int main(void){
    Pet myPet;
    strcpy(myPet.name,"Boris"); 
    strcpy(myPet.breed,"dog"); 
    myPet.dateOfBirth.day = 1;
    myPet.dateOfBirth.month = 4;
    myPet.dateOfBirth.year = 1988;
    
    etc...

    typedef struct point Point;

    struct point {
      double x;
      double y;
    };

• For each of these two representations, write a function which, given two points p and q, returns the distance between them.

      double distA( double p[2], double q[2] );
  
      double distS( Point p, Point q );
  

  Recall that the formula for the distance between 2 points is

  distance =  sqrt ((x2-x1)^2 + (y2-y1)^2)
  

  #include <math.h>
  
  double distA( double p[2], double q[2] ) {
    return( sqrt( ( p[0] - q[0] )*( p[0] - q[0] )
                 +( p[1] - q[1] )*( p[1] - q[1] )));
  }
  
  double distS( Point p, Point q ) {
    return( sqrt(  ( p.x - q.x )*( p.x - q.x )
                 + ( p.y - q.y )*( p.y - q.y ) ));
  }
  

  Do you find one version of the function "easier to read" than the other?

• Using the struct representation, write a function that reads in points from standard input and stores them in an array. It should return how many points it successfully read in. We will assume points are read in as pairs of integers separated by spaces and/or newlines.

  It should have the following prototype

  int readPoints(Point points[], int maxPoints);
  

  int readPoints(Point points[],int maxPoints){
      int i = 0;
      while ( i < maxPoints && 
              scanf("%lf %lf",&(points[i].x), &(points[i].y)) == 2){
                                 
          i = i + 1;
      }
      return i;
  }
  

• Write a function to print out an array of points. Print them out to 1 decimal place and in this format (4.5,9.0)

  void printPoints(Point points[], int numPoints){
      int i = 0;
      while ( i < numPoints ){
          printf("(%.1lf,%.1lf)",points[i].x,points[i].y);
          i = i + 1;
      }
      printf("\n");
  
  }
  

• Write a program that uses these 2 functions to read in a maximum of 100 points and print them out again.

  #define MAX_POINTS 100
  
  int main(void){
      Point points[MAX_POINTS];
      int numPoints = readPoints(points, MAX_POINTS);
      printPoints(points,numPoints);
      return EXIT_SUCCESS;
  }
  

• Write a function furthestFromOrigin that finds and returns the point in the array that is furthest from the origin. You can use your distS function from earlier.

  Point furthestFromOrigin(Point points[], int numPoints){
      Point origin;
      origin.x = 0;
      origin.y = 0;
     
      int maxIndex = -1;
      double maxDist;
      
      double dist;
      int i = 0; 
      while ( i < numPoints ) {
          dist = distS(origin, points[i]);
          if( maxIndex == -1 || dist > maxDist ){
              maxDist = dist;
              maxIndex = i;
          }
          i = i + 1;
      }
      if(maxIndex != -1 ){
          return points[maxIndex];
      } else {
          //will only happen if numPoints <= 0
          return origin;
      }
  }
  

#define MAX_PLATE
typedef struct parkingFine ParkingFine;
struct parkingFine{
    double amount;
    char numberPlate[MAX_PLATE];
};


int readParkingFine ( ParkingFine fine );

int main(void){
    ParkingFine f;
    if(readParkingFine(f)){
        printf("%lf %s\n",f.amount, f.numberPlate);
    } else {
        fprintf(stderr,"Invalid Input\n");
        return EXIT_FAILURE;
    }
    return EXIT_SUCCESS;
}

// Returns 1 if valid input was read in
// Returns 0 otherwise
int readParkingFine ( ParkingFine fine ){
    if ( scanf("%lf",&fine.amount) != 1 ||
         fgets(fine.numberPlate,MAX_PLATE,stdin) == NULL){
        return 0;
    } else {
        return 1;
    }
}

structs are passed by value, so a copy of the struct has been passed into the function, 
so any changes made to it do not affect the variable in the main function. 
To change this we could do the following and pass it in by reference by  passing in the address of the struct.

int readParkingFine ( ParkingFine * fine );

int main(void){
    ParkingFine f;
    if(readParkingFine(f)){
        printf("%lf %s\n",f.amount, f.numberPlate);
    } else {
        fprintf(stderr,"Invalid Input\n");
        return EXIT_FAILURE;
    }
    return EXIT_SUCCESS;
}

// Returns 1 if valid input was read in
// Returns 0 otherwise
// Note: fine->numberPlate is shorthand for (*fine).numberPlate
int readParkingFine ( ParkingFine * fine ){
    if ( scanf("%lf",&fine->amount) != 1 ||
         fgets(fine->numberPlate,MAX_PLATE,stdin) == NULL){
        return 0;
    } else {
        return 1;
    }
}

#define MAX_LEN 100

typedef struct student Student;

struct student{
    int zid;
    char name[MAX_LEN];
}

 Student * findStudent(Student class[], int size, int zid);   

Student * findStudent(Student class[], int size, int zid) {
    int i;
    
    for ( i = 0 ; i < size; i++){
        if( class[i].zid == zid){
            return &(class[i]);
        }
    }
    
    return NULL;
}