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 and c are invalid; b is valid but checks memory addresses, not content; d is valid.

Step-by-step solution

Understanding String Assignment

Statement a: `str1 = str2;` is attempting to assign one array to another directly. In C++, arrays do not support direct assignment like this, so this statement is invalid. String assignment must be done via functions like `strcpy()`.

Comparing String Pointers

Statement b: `if (str1 == str2)` compares the memory addresses of `str1` and `str2` rather than their contents. In C/C++, this is not a valid way to compare strings for equality. Use `strcmp()` for a content comparison.

Checking String Length

Statement c: `if (strlen(str1) >= strlen(str2)) str1 = str2;` uses `strlen()` to compare lengths correctly, but then tries to assign `str1 = str2` again, which is invalid. Use `strcpy()` if you need to copy the content of one string into another.

Using strcmp for String Comparison

Statement d: `if (strcmp(str1, str2) < 0)` uses `strcmp()` correctly. This statement is valid as it compares the two strings to determine their lexicographical order.

Key concepts

C++ Arrays

In C++, arrays are used to store a collection of elements of the same data type. For example, `char str1[15];` creates an array that can hold up to 15 characters. This is useful for storing strings in C++, which are essentially arrays of characters. However, it's important to note that the ' ' terminator used in strings takes up one of these character slots.

When dealing with arrays, there are some limitations. Specifically, you cannot assign one array to another directly using the `=` operator, as you would with simple variables. Instead, you must use a function to copy the arrays element by element if you want to assign values between them. Functions like `strcpy()` (found in the `` library) are specifically designed for this purpose. Using `strcpy(str1, str2);` copies the content of `str2` into `str1`. This concept is fundamental, especially when dealing with string arrays.

Arrays help manage data in a structured way, but require careful handling of indexing and memory. Always make sure that your operations on arrays respect the bounds of the array to avoid errors.

String Functions in C++

String functions in C++ are essential tools for managing strings. They provide you with ways to manipulate and query strings, which are represented as arrays of characters in C++. The `` library includes many such functions. Let's explore a few commonly used ones:

- **`strlen()`**: This function returns the length of a given C-style string (array). For instance, `strlen(str1)` gives you the number of characters in `str1`—excluding the null terminator. It’s useful for determining if you have enough space in your array before copying data into it.

- **`strcpy()`**: As mentioned earlier, `strcpy(destination, source)` copies the content from the source string to the destination. It’s crucial to ensure the destination array is large enough to hold the contents, including the null terminator.

These string functions are invaluable for performing operations on strings safely and efficiently in C++. By using them, you ensure better memory management and avoid common pitfalls like buffer overflow. Always verify that your C-style strings are null-terminated for these functions to behave correctly.

String Comparison in C++

Comparing strings in C++ is a critical operation that requires an understanding of how strings are represented in memory. Unlike languages that offer direct string comparison operators, C/C++ uses functions to handle C-style strings. Here, the `strcmp()` function from the `` library is the tool of choice.

- **`strcmp()`**: This function compares two strings lexicographically (dictionary order). You use it to determine if one string is less than, greater than, or equal to another. The syntax `strcmp(str1, str2)` works by returning an integer:

• `< 0` if `str1` is less than `str2`
• `0` if `str1` is equal to `str2`
• `> 0` if `str1` is greater than `str2`

This comparison is based on ASCII values of the characters, proceeding sequentially until a difference is found or the end of the strings is reached.

Using `strcmp()` effectively can help you write programs that accurately compare string data. Remember that `strcmp()` only works with null-terminated C-style strings. So, always ensure your strings are properly terminated. With this approach, you can carry out sophisticated string comparisons without running into common errors associated with direct memory address comparisons.