Question

Given the declaration: char str1[15]; char str2[15] = "Good day"; Mark the following statements as valid or invalid. If a statement is invalid, explain why. a. str1 = str2; b. if (str1 == str2) cout << " Both strings are of the same length." << endl; c. if (strlen(str1) >= strlen(str2)) str1 = str2; d. if (strcmp(str1, str2) < 0) cout << "str1 is less that str2." << endl;

Short answer

Statements a, b, and c are invalid. Statement d is valid.

Step-by-step solution

Evaluate statement (a)

The statement `str1 = str2;` tries to assign one array (str2) to another (str1) using the assignment operator `=`. This is invalid because arrays in C cannot be assigned directly like this. Instead, a loop or a function like `strcpy` should be used to copy the string.

Evaluate statement (b)

The statement `if (str1 == str2)` checks if the pointers that store the addresses of the arrays str1 and str2 are equal, not if the strings themselves are equal. This is invalid for comparing the content of the strings. Use `strcmp` to compare the content of two C-strings.

Evaluate statement (c)

The condition `if (strlen(str1) >= strlen(str2))` is valid as it correctly uses `strlen` to get the lengths of the strings. However, the following statement `str1 = str2;` is invalid for the same reason as in Step 1; string assignment like this is not allowed for arrays.

Evaluate statement (d)

The statement `if (strcmp(str1, str2) < 0)` is valid. It uses `strcmp` to compare str1 and str2 lexicographically, which is the correct function for this task in C. Since the statement after the condition only prints a message, it's valid as well.

Key concepts

Arrays in C++

In C++, arrays are a foundational concept that allow you to store multiple elements of the same type in one place. Arrays facilitate efficient data organization and manipulation. However, they come with certain limitations:

Arrays have a fixed size, which you must define at the time of declaration. For example, `char str1[15];` creates an array capable of holding 14 characters plus the null terminator.

Array elements are stored in contiguous memory locations, making them ideal for sequential access. But, this also means that direct assignment between arrays, such as with the `=` operator, is not possible in C or C++. This limitation arises because arrays are treated as pointers to their first element. If you want to copy the contents of one array into another, you must use a loop or a function like `strcpy`.

Despite this limitation, arrays remain essential for static collections of data, especially when performance is a critical factor. They allow quick access to elements and leverage the system's memory optimizing features.

String manipulation

In C++, string manipulation is a common task, especially when dealing with C-style strings or C-strings, which are arrays of characters. Unlike the more advanced `std::string` class, C-strings require manual handling for operations such as copying, comparing, or modifying.

To handle strings efficiently, consider functions like:

• strlen: Measures the length of a C-string by counting the number of characters until the null terminator.
• strcpy: Copies the content of one string to another. For instance, instead of using `str1 = str2;`, you would use `strcpy(str1, str2);`.
• strcat: Concatenates two strings. It appends one string onto the end of another.

C-string manipulation requires attention to memory limitations and proper termination of strings with a null character. Failure to manage these details can lead to unexpected behavior or errors in your program.

Comparison of C-strings

Comparing C-strings in C++ necessitates a different approach than that used for primitive data types or `std::string`. C-strings are compared based on their content rather than their memory addresses.

Using the `==` operator with C-strings checks if the pointers to their first elements are the same, which only happens if both variables point to the exact same memory location. Thus, this method does not compare content.

For proper content comparison, use the `strcmp` function, which compares two strings lexicographically. This function returns:

• A negative value if the first string is less than the second.
• Zero if the strings are equal.
• A positive value if the first string is greater than the second.

Understanding this function is crucial when designing conditions to evaluate or sort strings based on their lexicographical order.

C++ syntax rules

C++ syntax forms the structure of your code and dictates how you can combine elements to create functional programs. When working with arrays and strings, understanding the constraints and allowances of C++ syntax is vital.

Arrays use zero-based indexing, so accessing elements must fall within the bounds of the declared size. Overshooting this index boundary constitutes undefined behavior and could cause your program to crash.

Assignments with the `=` operator differ when dealing with arrays. Unlike primitive data types, arrays cannot directly be assigned from another array. To circumvent this, you should utilize functions specifically designed for array operations.

When writing conditions and performing loops, brackets `{}` define the block of code to execute, while semicolons `;` terminate statements. Incomplete use or misuse of these elements can disrupt the flow of your program, leading to logic errors or compile-time failures.

Understanding and applying these rules help maintain a robust and error-free code base that adheres to C++ conventions.