Compiling C Programs with gcc in linux

In linux, use gcc to compile the C program-general Linux technology-Linux programming and kernel information. For details, refer to the following section. Void main ()
{Float x, y, z,;
Scanf ("% f, % f, % f", & x, & y, & z );
A = (x + y + z)/3;
Printf ("% f \ n", );
}
I saved the above program as: 1.c, and put it to the desktop. Then, I went to the desktop gcc-o 1. c under the terminal and executed it:
Jimoon @ jimoon-1 :~ /Desktop $ gcc-o 1 1.c
1. c: In the 'main' function:
1. c: 3: Warning: Implicit declaration of incompatible built-in function 'scanf'
1. c: 5: Warning: Implicit declaration of incompatible built-in function 'printf'
1. c: 2: Warning: The return type of 'main' is not 'int'
A file named "1" is displayed on the desktop.
Can you ask why? How to compile C Programs in linux