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Magazine Chapter 9: Problem 26
Given the declaration: char string15 [16]; mark the following statements as valid or invalid. If a statement is invalid, explain why. a. strcpy(string15, "Hello there"); b. strlen(string15); c. string15 = "Jacksonville"; d. cin >> string15; e. cout << string15; f. if (string15 >= "Nice day") cout << string15; g. string15[6] = 't';
Short Answer
Expert verified
a, b, d, e, g are valid; c and f are invalid.
Step by step solution
01
Validate Statement a
The statement `strcpy(string15, "Hello there");` is valid. The `strcpy` function copies the string "Hello there" into the `string15` array. The array `string15` is large enough to contain the copied string, which has 12 characters, plus a null terminator, bringing the total to 13, which fits within the 16-character limit.
02
Validate Statement b
The statement `strlen(string15);` is valid. The `strlen` function calculates and returns the length of the string stored in the `string15` array without the null terminator, and it's perfectly valid to use it on the array.
03
Evaluate Statement c
The statement `string15 = "Jacksonville";` is invalid. In C++, you cannot directly assign a string literal to an array once it has been declared. You must use a function like `strcpy` to copy a string to a character array.
04
Validate Statement d
The statement `cin >> string15;` is valid if you want to read a word into the `string15` array. Note that this reads input only up to the first whitespace (space, newline, or tab) and will not check for overflow.
05
Validate Statement e
The statement `cout << string15;` is valid. This statement prints the contents of the `string15` array to standard output.
06
Evaluate Statement f
The statement `if (string15 >= "Nice day") cout << string15;` is invalid. The comparison `string15 >= "Nice day"` is not valid in the case of C-style strings, as the `>=` operator is not defined for arrays. You need to use `strcmp` to compare C-style strings.
07
Validate Statement g
The statement `string15[6] = 't';` is valid. This statement sets the character at index 6 of the `string15` array to 't', which is permissible as long as you're within bounds.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Array Manipulation
In C++, character arrays, such as `char string15[16];`, are used to handle sequences of characters, much like strings. However, they require specific handling methods. For beginners, remembering that manipulating these arrays means directly handling individual character elements is crucial. Here are key points about array manipulation with character arrays:
- Character arrays are often used for fixed-size character storage.
- They do not possess built-in methods like modern C++ strings (`std::string`) do. Hence, functions from the `cstring` library like `strcpy` are employed to manipulate them.
- Direct assignment to an entire array, like in the statement `string15 = "Jacksonville";`, is invalid. Assignments must be done element by element or through functions like `strcpy`.
- It's important to ensure that operations do not exceed the array's size, as C++ does not automatically manage overflow protection.
String Functions
While character arrays are a fundamental aspect of C++, their manipulation is often facilitated by string functions from the C standard library. These functions include helpers for copying, comparing, and measuring strings:
- `strcpy`: Used to copy one string into another, it is crucial when handling character arrays. For example, `strcpy(string15, "Hello there");` copies "Hello there" into the `string15` array.
- `strlen`: This computes the length of a string, excluding the null terminator. In the context of `strlen(string15);`, it measures how many characters are in `string15` that form a valid string.
- Many other functions such as `strcat`, `strncpy`, and more offer powerful ways to handle strings within given constraints.
Comparison Operations
When dealing with character arrays, comparisons can often lead to confusion. In C++, direct comparison operations like `==`, `>=`, or `!=` are not inherently defined for comparing C-style strings (character arrays).
- Statements like `if (string15 >= "Nice day")` are invalid, as arrays are not compared by their contents but by their addresses, resulting in unintended behavior.
- Instead, use the `strcmp` function from the `
` library to compare two character arrays by comparing them character by character. - `strcmp(string15, "Nice day")` returns 0 if the strings are equal, a negative value if `string15` is less than "Nice day", and a positive value if greater, making it the correct approach for comparing such strings.
Character Indexing
Indexing in C++ character arrays is a direct and straightforward process. Each character element of the array can be accessed or modified using its index, akin to accessing elements in a list.
- Character arrays have zero-based indexing, so the first element is accessed with an index of `0`, the second with `1`, and so on.
- To change a character at a specific position, simply assign a new value at that index, as demonstrated by `string15[6] = 't';`. This sets the seventh character to `t`.
- Indexing is done within the bounds of the array's declared size to prevent potential segmentation faults or data corruption. For `string15`, indices 0 through 15 are valid.
