Question

Determine whether the following array declarations are valid. If a declaration is invaid, explain why. a. int 1 ist 75; b. int size; double list [size]; c. int test [-10]; d. double sales [40.5];

Short answer

Declarations a, b, c, and d are invalid due to naming, non-constant size, negative size, and non-integer size issues, respectively.

Step-by-step solution

Validate Declaration of 'a'

The first declaration is `int 1 ist 75;`. The issue here is that variable names in most programming languages cannot begin with a number. Therefore, it is an invalid declaration.

Validate Declaration of 'b'

The next declarations are `int size;` and `double list [size];`. Here, `size` is an integer variable, but array size declarations in most programming languages require a constant integer value. Therefore, `list` is an invalid array declaration because `size` is not a constant.

Validate Declaration of 'c'

The declaration `int test [-10];` attempts to create an array with a negative size. Array sizes must be positive integers. Therefore, it is invalid.

Validate Declaration of 'd'

The declaration `double sales [40.5];` is attempting to use a non-integer value for the array size. Array sizes must be whole numbers, hence this declaration is also invalid.

Key concepts

Invalid Variable Names in C++

In C++, variable names play a crucial role in identifying different elements within a program. It is essential to understand the rules that govern these names to avoid errors. One of the most fundamental rules is that a variable name cannot begin with a number. This rule is aimed at reducing confusion between variable names and numerical values.

Additionally, variable names:

• Can only contain letters, numbers, and underscores.
• Must not contain spaces or special characters.
• Should be meaningful, to make the code easier to read and understand.
• Are case-sensitive, meaning `Variable` and `variable` would be distinct identifiers.

Following these guidelines ensures the proper functioning and readability of your C++ code.

Array Size Requirement in C++

When declaring an array in C++, the size of the array must be specified at the time of declaration as a constant integer. This requirement is necessary for the compiler to allocate memory for that array.

Consider the declaration:

• `double list [size];`

Here, `size` should be a constant value rather than an integer variable because variables can change their value at run-time, which conflicts with the need for the compiler to determine the memory space at compile-time.

Using a constant, like `const int size = 10;`, ensures that the array size remains fixed and correct.

Negative Array Size

In C++, an array cannot have a negative size. Array sizes represent the amount of storage required to hold the array elements, and logically this cannot be negative.

For example, `int test [-10];` is invalid because:

• Negative values have no physical interpretation regarding memory allocation.
• C and C++ languages restrict memory allocation only to positive integral values.

To resolve this issue, always ensure that the size of the array is specified as a positive integer.

Non-integer Array Size

The size of an array in C++ must be specified using integer values. This means the array size should be a whole number without any fractional components.

The declaration `double sales [40.5];` is incorrect as 40.5 is not an integer:

• The compiler needs a whole number to determine the exact block of memory required.
• Fractions or decimal points do not make logical sense in terms of indexing the array elements.

A correct approach is to round the number to the nearest whole number, or before declaration, use values like 40 or 41 to represent the size, ensuring it is an integer.