c - arguments of main? -

i know signature of main is:

int main(int argc, char **argv); 

but don't know why main work too:

main(a){} 

what's 'a' doing here? why compiler don't show error?? because havn't declare 'a' before use it.

it's feature of older c code called "implicit int". variable type not specified assumed int. similarly, function return type not specified assumed return int. it's considered deprecated, becomes useful in obfuscated code , code golf.

so should read as

int main(int a) {} 

where ints have been omitted because implicit.

as whozcraig mentions, standards point-of-view not conforming , not portable. pragmatically, lot of compilers let away when not in standards-conformance mode.

implicit int behavior doesn't out of declaring variables, however.

main(a){     b,c; // int declarations     c = 5;     b = c + 10;     d = b; // no! d not declared you, implicit int happening.     return 0; }