I'm getting NAN out of nowhere

[flamencofantasy via Digitalmars-d-learn]

On Thursday, 9 July 2015 at 15:14:43 UTC, Binarydepth wrote:
> This is my code :
> import std.stdio : writeln, readf;
> void main()	{
> 	int[3] nums;
> 	float prom;
> 	foreach(nem; 0..2)	{
> 		writeln("input a number : ");
> 		readf(" %d", &nums[nem]);
> 		prom+=nums[nem];
> 	}
> 	writeln(prom/3.0);
> }
>
> I get prompted two times for a number and I then get NAN out of 
> nowhere.

foreach(nem; 0..3)