GCC: Compilation using C/C++

[Ricardo Sardano Guanciale]

My name is Ricardo, please can you help me?

How can I compile the following ANSI C code without warnings:

#include <stdio.h>

void main(void)
{
     printf("Hello world!\n");
}

I tryed:

gcc helloworld.c -o helloworld

The compiler answered:

helloworld.c: In function `main':
helloworld.c:4: warning: return type of 'main' is not `int'

I also tryed:

gcc -ansi helloworld.c -o helloworld

But...with the same warnings.

Other problem is with this C++ code:

#include <iostream>

void main(void)
{
     cout << "Hello world!\n";
}

gcc helloworld.cpp -o helloworld

The compiler answered:

helloworld.cpp:4: error: `main' must return `int'
helloworld.cpp: In function `int main(...)':
helloworld.cpp:5: error: `cout' undeclared (first use this function)
helloworld.cpp:5: error: (Each undeclared identifier is reported only 
once for each function it appears in.)

I also tryed:

gcc -ansi helloworld.cpp -o helloworld

But...with the same warnings.

Please these are basic ANSI C/C++ samples that I would like to compile 
using gcc.

Please can you help me?

Thank you very much and best regards,

Ricardo