Question

Find the error in each of the following: a. Assume that struct Card has been defined as containing two pointers to type charnamely, face and suit. Also, the variable c has been declared to be of type Card, and the variable cPtr has been declared to be of type pointer to Card. Variable cPtr has been assigned the address of c. cout << *cPtr.face << endl; b. Assume that struct Card has been defined as containing two pointers to type charnamely, face and suit. Also, the array hearts[ 13 ] has been declared to be of type Card. The following statement should print the member face of element 10 of the array. cout << hearts.face << endl; c. struct Person { char lastName[ 15 ]; char firstName[ 15 ]; int age; } d. Assume that variable p has been declared as type Person and that variable c has been declared as type Card. p = c;

Short answer

Correct errors in part (a) with 'cout << *(cPtr->face) << endl;', in part (b) with 'cout << hearts[10].face << endl;', and part (d) cannot assign different structured types.

Step-by-step solution

Understanding the structure and variable declaration

In part (a), we need to determine how struct Card is defined and how variables are declared. The struct Card contains two pointers to char: face and suit. The variable c is a Card instance and cPtr is a pointer to Card, pointing to c.

Analyze the error in accessing struct members using pointers

In part (a), the line 'cout << *cPtr.face << endl;' attempts to dereference the 'face' member directly, which is incorrect since cPtr is a pointer to Card. The correct method is to use parentheses to dereference the entire structure first, or use the arrow operation '->'. Correct syntax: 'cout << *(cPtr->face) << endl;' or 'cout << (*cPtr).face << endl;' if face needs indirect access.

Problem with array and struct member access

In part (b), the array hearts is declared as type Card, which is correct. However, accessing a member of a specific element of this array to print it, is done incorrectly. The correct way to access the face of the 10th element is: 'cout << hearts[10].face << endl;'.

Struct definition correctness

In part (c), the struct Person has been correctly defined with an array of char for lastName and firstName, and an integer age. There are no problems with the definition of struct Person.

Incompatible assignment of different structs

In part (d), there is an attempt to assign a struct of type Card to a struct of type Person with 'p = c;'. This is not possible because these are different types, and their data cannot be directly copied or assigned in such a manner.

Key concepts

Pointers and References

Pointers and references in C++ can be a bit tricky at first, but once you have a handle on them, they help create efficient and powerful programs. Pointers are variables that store memory addresses, often pointing to other variables. In C++, you can use pointers to directly manipulate memory.
In the given exercise, the struct `Card` includes pointers to `char` for its `face` and `suit` members. The problem in part (a) arises because you must correctly access these members using the `cPtr` pointer to the `Card` object. Since `cPtr` is itself a pointer to the entire `Card` object, accessing the `face` member requires dereferencing correctly.
You may either use:

• The arrow operator: `cPtr->face` which automatically dereferences the pointer and accesses `face`
• Or use parentheses to ensure proper processing: `(*cPtr).face`

Both of these expressions provide the same functionality, optimizing ease of access and readability in the code.

Array of Structs

An array of structs is a highly useful construct in C++, facilitating the storage of multiple structured items in a clean and organized manner.
The exercise showcases a common mistake in part (b), where an array of structs named `hearts` is declared. This array holds `Card` objects, capable of storing information for cards in a deck of cards. To correctly access and manipulate each element in the array, knowledge of syntax and index is essential.
When you want to access the `face` member of the 10th element of the `hearts` array, you need to first identify the correct element, using the index `hearts[10]`. Then, you should access the `face` member directly, as in:

• `cout << hearts[10].face << endl;`

Using the dot operator `.` is standard practice when accessing members directly within elements of a struct array. This ensures that the code accesses the correct member reliably and efficiently.

Struct Assignment Error

Struct assignment involves copying data from one struct variable to another, provided they are of the same type. If the types differ, as seen in part (d) of the exercise, you'll encounter an error.
C++ has very strict rules regarding the assignment of structs. Each struct type is distinct, defined by its member types and arrangements. Even if two structs seem similar, their types must match exactly to facilitate assignment.
In part (d), there's an attempt to assign a struct `Card` to a struct `Person`. This assignment can't be performed because:

• `Card` and `Person` are different data types.
• Each struct contains a different set of data members.
• Structs in C++ lack built-in mechanisms to convert one type to another.

To resolve such issues, ensure that assignments between structs only occur when they are the same type, or use conversion functions to adapt data appropriately between distinct struct types.