To elaborate on what Tamas said, it’s a convention in Julia that types (and hence their constructors) start with an uppercase letter, while all other functions are lowercase. What you’re seeing here is that there is a convenience function which converts the argument to a floating point type
julia> float(BigInt(1))
1.0
julia> typeof(ans)
BigFloat
while there isn’t a function to convert the argument to a generic integer type. This is probably because a floating point number can’t generally be “converted” to an integer, you likely want to round it in some ways, but you must be explicit about it by using functions like round, floor, ceil, etc…