The most important part of a program written in C is the main() function.

In C, there are two types of functions:

Built-in functions
Custom (user-defined) functions

Every C program must include the main() function.

The difference between a command and a function is the presence of parentheses, for example:

main();
calcIt();
printf();
strlen();

Commands come without parentheses:

return
while
int
iffloat

If a function name consists of multiple words, it should follow the camelCase format.

For example:

doReportPrint();
calcIt();

The main() function name, as well as most built-in C function names, should only contain lowercase letters.

Even if the main() function is not listed first in your program, it still defines the entry point of program execution.

After the keyword main(), an opening curly brace { always follows.

The closing curly brace marks the end of the main() function block.

The expression #include <stdio.h> should be included in almost every C program, as it helps with outputting to the screen and receiving input.