Explanation:
The program execution always starts from the main function in C and C++ programming languages. Here is a detailed explanation:

Main Function:
- The main function is the entry point of a C or C++ program.
- It is a predefined function that serves as the starting point for program execution.
- The main function is required in every C and C++ program.
- When the program is executed, the operating system calls the main function to begin executing the program.

User-defined Function:
- User-defined functions are functions created by the programmer to perform specific tasks.
- These functions are called within the main function or other functions depending on the program's logic.
- While user-defined functions play a crucial role in structuring the program, they are not the starting point of program execution.

Void Function:
- Void functions are functions that do not return a value.
- These functions can be called within the main function or other functions to perform specific actions.
- Similar to user-defined functions, void functions are not the starting point of program execution.

Else Function:
- The term "else function" is not a standard programming concept.
- The else keyword is typically used in conditional statements like if-else statements.
- Conditional statements are used to control the flow of the program based on certain conditions but do not serve as the starting point of program execution.
In conclusion, the main function is where the execution of a C or C++ program starts. It is the entry point that the operating system calls to begin executing the program.