int 'function name', then later just type 'function name()'
the 'int' depends on what the function should return. The function which divides its argument by 2 should return a 'double', so "double function( double arg)" , the function 'function1' does not return anything (or returns a void) and does not take arguments (or a void argument list), so " void function1( void)".

Experiment a little....