Constant truncated to integer

The following GO program gives the error:

./fft.go:13: constant -6.28319 truncated to integer
./fft.go:13: cannot use -7 * k / N (type int) as type float64 in assignment

Program:

package main
import (
	"math"
	"fmt"
)
func main() {
	fmt.Println("Hello world ",math.E)
	var k, N int = 1, 10
	var ans float64 = 0
	var c float64 = (-2.0 * math.Pi * k) / N
	x := make([]float64,N)
	for i := 0; i < len(x); i++ {
		x[i] = 1
	}
	ans = 0
	for i := 0; i < N; i++ {
		ans += x[i] * math.E
	}
	fmt.Println(ans)
}

Why cant I use an int in a type of float64 ?

Replace

var c float64 = (-2.0 * math.Pi * k) / N

by

var c float64 = (-2.0 * math.Pi * float64(k)) / float64(N)

To quote the spec:

> Conversions are required when different numeric types are mixed in an
> expression or assignment. For instance, int32 and int are not the same
> type even though they may have the same size on a particular
> architecture.

Go uses static typing and doesn't automatically convert between numeric types. The reason is probably to avoid some errors. For instance, what value and what type should float64(2.5) * int(2) yield? Should the result be int(5)? int(4)? float64(5.0)? In Go, this isn't an issue. The Go FAQ has more to say on this.

@jnml points out that, in this case, the following is enough:

var c float64 = -2 * math.Pi / float64(N)