sum() - return the sum of all of the passed int or float parameters
int|float sum( int|float... );
This function will aggregate the values of all arguments into a single
return value. The arguments may be any combination of int or float and
the appropriate type will be returned based on the final total.
sum( 1, 2, 3, 4, 5, 6 ); // Result: 21
sum( 1, 2, 3.5, 4, 5, 6 ); // Result: 21.500000
array_sum