Exercise Solutions

Concept Questions

Question 1

Parallel arrays are multiple arrays where data stored at the same index across arrays represents a single entity. Items stored at the same index are considered to be part of the same entity

Example:

int productID[50] = {101, 102, 103};
float price[50] = {185.50, 9.95, 16.30};
int inventory[50] = {5, 10, 6};

Here, ProductID[0], price[0], and inventory[0] all refer to the same Product.

Product #101 sells for $185.50 and there are 5 in stock.

Question 2

• Maintenance: Adding an extra piece of information requires the addition of another array which may need involve altering function prototypes
• Synchronization: When modifying data (sorting, swapping), you must perform the same operation on all arrays to maintain parallelness; forgetting to update one array causes data corruption
• Scalability: As the number of related fields increases, the code becomes increasingly complex and error-prone
• Clarity: The relationship between arrays is implicit and not enforced by the language, making code harder to understand

Question 3

Arrays can be stored as members within a struct by declaring them as data members. Putting related arrays together into a struct allows related data to be packaged into one entity. This allows:

• grouping together related data
• parameter passing is simplified, pass in the address of the struct and the related data will all be there
• makes the code more readable as you are identifying how data is related logically

Question 4

part a

printf("%f", student1.assignments[2]);

part b

student1.exams[1] = 78.5

Question 5

• Struct with array members: A single struct that contains array data members

  struct CourseGrades
  {
      int studentID;
      float assignments[5];
  };

• Array of structs: An array where each element is a struct

  struct CourseGrades students[50];

The key difference is that a struct with array members is describing a single logical entity. An array of structs is multiple instances of a logical entity.

Question 6

part a

struct CourseGrades
{
    int studentID;
    float assignments[5];
    float exams[3];
};

part b

struct CourseGrades myclass[3] ={
    {101,{85.0, 90.0, 88.0, 92.0, 87.0}, {78.5, 82.0, 85.5}},
    {102, {92.0, 95.0, 91.0, 93.0, 94.0}, {88.5, 90.0, 92.5}},
    {103, {78.0, 80.0, 79.0, 81.0, 80.0}, {75.5, 77.0, 76.5}}
};

Question 7

struct EmployeeInfo
{
  int employeeID;
  char name[101];
  double salary;
  int performance[12];
}
...

//array of 50 structs, each representing an employee
struct EmployeeInfo employees[50];

Here, an array of structs would be better in this case. In total we must store:

• employeenumber
• name
• salary
• 12 ratings

In total there are 15 pieces of data for each employee. This is a lot of information. we would need 15 arrays to do this and that is going to make things extremely cumbersome.

Walkthrough

Exact Output:

2 -1 4 -2 1 -1
struct

Debugging

Syntax Errors

• declaration for parameters high and low are not correct
• assingment to high and low is the address-of operator instead of the dereferencing operator *high = highest for example instead of &high = highest
• temps is a single struct not an array in prototype
• temps[dayNumber] is a Temperature struct, we need to access the temperatures array within the struct
• missing semi colons inside the statements in the if blocks
• temps is misspelled as temp inside the loop

Logical Errors

• when you pass an array into a function you need to pass in how much of the array is being used. We are missing an argument that would provide that information
• dayNumber is not index. dayNumber is stored as a member of the struct. We need to find the struct with the matching day number then access that
• temperatures can be all negative. setting the highest to 0 would mean that no temperature in the array will ever be higher than that value (making 0 the highest value). We need to initialize highest with first element of array
• temperatures can be all positive. setting the lowest to 0 would mean that no temperature in the array will ever be lower than that value (making 0 the lowest value). We need to initialize lowest with first element of array

Stylistic Flaws

• if() statements should be bracketed even if there is only one statement
• open curly bracket for function should be on next line

Corrected Program

#include <stdio.h>

struct Temperature
{
    char dayNumber;
    float temperatures[24];
};

//fixes: made temps into an array, added argument called used to prototype, fixed syntax for
//pointers high and low
void getHighLow(int dayNumber, struct Temperature temps[], int used, int* high, int* low)
{


    float lowest;
    float highest;
    int i;
    int idx = -1;  //add variable to track where the matching dayNumber was found

    //find a struct with a matching dayNumber first, idx is the location
    //of the matching struct in the array
    for (i = 0; i < used && idx == -1; i++){
        if (temps[i].dayNumber == dayNumber){
            idx = i;
        }
    }

    //initialize lowest and highest using first element
    lowest = temps[idx].temperatures[0];
    highest = temps[idx].temperatures[0];

    //starting loop at 1 because we already set up the
    //lowest/highest with first element so we don't need to
    //look at it
    for (i = 1; i < 24; i++){
        //fix the access to access element idx of temps
        //also access data member temperature
        if (temps[idx].temperatures[i] > highest){
            highest = temps[idx].temperatures[i];
        }
        if (temps[idx].temperatures[i] < lowest){
            lowest = temps[idx].temperatures[i]
        }
    }

    //fix assignment
    *high = highest;
    *low = lowest;
}

Programming

part a

struct Product
{
    int id;
    char name[51];
    float price;
    int quantity;
};

part b

float totalValue(const struct Product* product)
{
    return product->price * product->quantity;
}

part c

int findProduct(const struct Product products[], int numProducts, int productID)
{
    int i;
    for (i = 0; i < numProducts; i++){
        if (products[i].id == productID){
            return i;
        }
    }
    return -1;
}

part d

void displayInventory(const struct Product products[], int numProducts)
{
    int i;
    for (i = 0; i < numProducts; i++){
        printf("ID: %d | Name: %s | Price: $%.2f | Qty: %d | Total: $%.2f\n",
               products[i].id, products[i].name,
               products[i].price, products[i].quantity,
               totalValue(&products[i]));
    }
}