What is command line argument?

Brain Kernighan.

Brian Wilson Kernighan is a Canadian computer scientist. He worked at Bell Labs and contributed to the development of Unix alongside Unix creators Ken Thompson and Dennis Ritchie. Kernighan's name became widely known through co-authorship of the first book on the C programming language with Dennis Ritchie.

Born: 1 January 1942 (age 80 years), Toronto, Canada

Nationality: Canadian

A virtual address is composed of the selector and offset.

A near pointer doesn't have explicit selector whereas far, and huge pointers have explicit selector. When you perform pointer arithmetic on the far pointer, the selector is not modified, but in case of a huge pointer, it can be modified.

These are the non-standard keywords and implementation specific. These are irrelevant in a modern platform.

The typecasting is a process of converting one data type into another is known as typecasting. If we want to store the floating type value to an int type, then we will convert the data type into another data type explicitly.

(type_name) expression;  

The fopen() function is used to open file whereas fclose() is used to close file.