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If a variable is used FREQUENTLY, it should be DECLARED with the register storage SPECIFIER, and the compiler MAY allocate a CPU register for its storage to speed up variable lookup.

Enumeration, also known as Enum in C, is a user-defined data type. It consists of constant integrals or integers that have names assigned to them by the user. Because the integer values are NAMED with enum in C, the WHOLE program is simple to learn, understand, and MAINTAIN by the same or even DIFFERENT programmer.

Macro on a high-level copy-paste, its definitions to places WHEREVER it is called. Due to which it saves a lot of time, as no time is SPENT while PASSING the control to a new function and the control is always with the CALLEE function. However, one downside is the size of the compiled binary is large but once compiled the program comparatively runs faster.

Typecasting is the PROCESS to convert a VARIABLE from one datatype to another.  If we WANT to STORE the large type VALUE to an int type, then we will convert the data type into another data type explicitly.

Syntax: (data_type)expression;

For Example:

n++ being a unary operation, it just needs one variable. Whereas, n = n + 1 is a BINARY operation that adds overhead to take more time (also binary operation: n += 1). However, in modern platforms, it depends on few things such as PROCESSOR architecture, C compiler, usage in your code, and other factors such as hardware problems.

While in the modern compiler even if you write n = n + 1 it will get CONVERTED into n++ when it goes into the optimized binary, and it will be EQUIVALENTLY efficient.

In C, a POINTER can also be used to store the address of another pointer. A double pointer or pointer to pointer is such a pointer. The address of a VARIABLE is STORED in the FIRST pointer, whereas the address of the first pointer is stored in the second pointer.

The syntax of declaring a double pointer is GIVEN below:

• CONST CHAR* P is a POINTER to a const char.
• char const* p is a pointer to a char const.

Since const char and char const are the same, it's the same.

A pointer is a variable that stores or POINTS to ANOTHER variable's address. The VALUE of a variable is STORED in a normal variable, WHEREAS the address of a variable is stored in a pointer variable.

The difference between this is in scope. A truly global variable has a global scope and is visible everywhere in your program.

global_temp is a global variable that is visible to everything in your program, although to make it visible in other modules, you'd need an ”extern int global_temp; ” in other source files if you have a multi-file project.

A static variable has a LOCAL scope but its variables are not ALLOCATED in the stack segment of the memory. It can have less than global scope, although - like global variables - it RESIDES in the .bss segment of your COMPILED binary.

After you compile the C SOURCE, the symbol names NEED to be intact in the object code. If we introduce function overloading in our source, we should also provide name mangling as a preventive measure to avoid function name CLASHES. Also, as C is not a strictly TYPED language many things(ex: data types) are CONVERTIBLE to each other in C. Therefore, the complexity of overload resolution can introduce confusion in a language such as C.

When you compile a C source, symbol names will remain intact. If you introduce function overloading, you should provide a name mangling technique to prevent name clashes. Consequently, like C++, you'll have machine-generated symbol names in the compiled binary.

Additionally, C does not feature strict typing. Many things are implicitly convertible to each other in C. The complexity of overload resolution rules could introduce confusion in such kind of language

When a FUNCTION in C calls a copy of itself, this is KNOWN as recursion. To put it another way, when a function calls itself, this TECHNIQUE is CALLED Recursion. Also, this function is known as RECURSIVE function.

Syntax of Recursive Function:

The FUNCTION takes a pointer to an array of char elements that NEED to be converted, and a FORMAT string needs to be written in a buffer as a string

The output after running the above code:

Output: Value of Pi = 3.141593

The FUNCTION takes the string as an input that needs to be converted to an integer.

Return Value:

• On successful conversion, it RETURNS the desired integer value
• If the string STARTS with alpha-numeric char or only contains alpha-num char, 0 is returned.
• In case string starts with numeric character but is followed by alpha-num char, the string is converted to integer till the FIRST occurrence of alphanumeric char.

In C, #line is used as a preprocessor to re-set the line number in the code, which TAKES a parameter as line number. Here is an example for the same.

A preprocessor is a SOFTWARE program that processes a source file before sending it to be COMPILED. INCLUSION of header files, macro expansions, conditional compilation, and LINE control are all possible with the preprocessor.

The most commonly used built-in FUNCTIONS in C are sacnf(), printf(), strcpy, strlwr, STRCMP, strlen, strcat, and many more.

Built-function is also known as library functions that are PROVIDED by the system to make the life of a developer easy by ASSISTING them to do certain commonly used predefined tasks. For example, if you need to PRINT output or your program into the terminal, we use printf() in C.

The answer is 'f'.

Explanation: The STRING mentioned "abxdef" is an array, and the  EXPRESSION is EQUAL to "abxdef"[5]. Why is the inside-out expression equivalent?  Because a[b] is equivalent to *(a + b) which is equivalent to *(b + a) which is equivalent to b[a].

• printf() is used to print the output on the DISPLAY.
• scanf() is used to read formatted data from the keyboard. 

Some datatype format SPECIFIERS for both printing and SCANNING purposes are as follows:

• %d: It's a datatype format specifier for printing and scanning an integer value. 
• %s: It's a datatype format specifier for printing and scanning a string. 
• %C: It's a datatype format specifier for displaying and scanning a character value.
• %F: The datatype format specifier %f is used to display and scan a float value.

Some features of the C language are- 

1. It is Simple And EFFICIENT. 
2. C language is PORTABLE or Machine Independent.
3. C is a mid-level Programming Language. 
4. It is a structured Programming Language.
5. It has a function-rich library. 
6. Dynamic Memory Management.
7. C is super fast.
8. We can use POINTERS in C.
9. It is extensible.

C has characteristics of both assembly-level i.e. low-level and higher-level languages. So as a result, C is COMMONLY CALLED a middle-level language. Using C, a USER can write an operating system as well as CREATE a menu-driven consumer billing system.