What is #define used for in C?

The #define creates a macro, which is the association of an identifier or parameterized identifier with a token string. After the macro is defined, the compiler can substitute the token string for each occurrence of the identifier in the source file.

Is typedef faster than define?

No difference in execution time, so you should be fine using either for competitive programming. I personally avoid #define and use typedef for types as it is more cleaner and readable.

What is the use of typedef in C?

typedef is a reserved keyword in the programming languages C and C++. It is used to create an additional name (alias) for another data type, but does not create a new type, except in the obscure case of a qualified typedef of an array type where the typedef qualifiers are transferred to the array element type.

What is the difference between macro and typedef in C?

We can have symbolic names to datatypes using typedef but not to numbers etc. Whereas with a macro, we can represent 1 as ONE, 3.14 as PI and many more. We can have a type name and a variable name as same while using typedef. Compiler differentiates both.

Can we use #define inside main?

You can use it inside a function, but it is not scoped to the function. So, in your example, the second definitions of a macro will be a redefinition and generate an error.

Can #define value be changed?

Yes, you can change a #define value.

What is the difference between const and #define in C?

#define is a preprocessor directive. Data defined by the #define macro definition are preprocessed, so that your entire code can use it. This can free up space and increase compilation times. const variables are considered variables, and not macro definitions.

Is typedef a storage class?

typedef is categorized as a storage class specifier because of similarities in syntax rather than functionality and because a typedef declaration does not allocate storage.

What is the difference between typedef struct and struct?

Basically struct is used to define a structure. But when we want to use it we have to use the struct keyword in C. If we use the typedef keyword, then a new name, we can use the struct by that name, without writing the struct keyword.

What is the point of typedef?

typedef is a keyword in the C and C++ programming languages. The purpose of typedef is to assign alternative names to existing types, most often those whose standard declaration is cumbersome, potentially confusing, or likely to vary from one implementation to another.