The getchar() function reads a single character from standard input (the keyboard) and returns it. It is one of the simplest input functions in C and a great way to understand how the input buffer works. In this program we use getchar() in a loop to read text entered by the user and count how …
Combinations and permutations in C are computed using two related formulas. A combination C(n, r) counts the number of ways to choose r items from n items where order does not matter. A permutation P(n, r) counts the number of ways to arrange r items chosen from n items where order matters. C(n, r) = …
C preprocessor directives are instructions that run before compilation. The preprocessor reads your source file, processes every line that starts with #, and hands the result to the compiler. Understanding them well means smaller code, safer constants, conditional compilation for different platforms, and header files that include safely more than once. Object-Like Macros — #define …
The ctype.h header provides a set of functions for testing and converting individual characters. Each function takes an int (the ASCII value of a character) and returns a non-zero value (true) if the character belongs to a certain class. They are used in parsers, tokenizers, input validation, and any code that processes text character by …
The extern keyword in C declares that a variable or function exists — but is defined somewhere else. It tells the compiler “trust me, this symbol is defined in another translation unit; the linker will resolve it.” Understanding extern is essential for any multi-file C program, and confusing declaration with definition is one of the …
The sizeof operator in C returns the size in bytes of a type or expression. It is evaluated at compile time and is the standard, portable way to determine how much memory any type occupies on the current platform. Because type sizes vary between 32-bit and 64-bit systems and between compilers, you should always use …