Question

The ____________ file must be included in a program that uses character testing functions.

Short answer

Answer: The header file `ctype.h` should be included in a C program to use character testing functions. Its purpose is to provide a set of functions to classify and transform individual characters, such as checking if a character is alphanumeric, a letter, or a digit.

Step-by-step solution

Identify the purpose of character testing functions

Character testing functions are used to check whether a given character belongs to a certain category. For example, they can be used to test if a character is a digit, an uppercase letter, or a whitespace character.

Identify the header file

In the C programming language, the character testing functions are defined in the header file `ctype.h`. This library contains a set of functions to classify and transform individual characters, such as checking if a character is alphanumeric, a letter, or a digit.

Include the necessary header file

To use the character testing functions in a program, the `ctype.h` header file must be included at the beginning of the source code. To do this, simply add the following line at the beginning of the program: ```c #include ``` Now, the program can use various character testing functions like `isalpha()`, `isdigit()`, `isupper()`, `islower()`, `isspace()` and more.