C program always starts with main function. The main function is the entry point of a C program, where the execution of a program starts. It is a user-defined function that is mandatory for the execution of a program because when a C program is executed, the operating system starts executing the statements in the main() function. Semocolon(;) is used to terminate every statment in C language.

#include <stdio.h>
        int main()
        {
            /* code */
            printf("Hello world");
        }