You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: utils.go
    path of file: ./repos/learning/golang/source_code/Go语言核心编程代码/chapter06/fundemo01/utils
    
    the code of the file until where you have to start completion: package utils 
import (
	"fmt"
)

var Num1 int = 300
//将计算的功能，放到一个函数中，然后在需要使用，调用即可
//为了让其它包的文件使用Cal函数，需要将C大
    
func Cal(n1 float64, n2 float64, operator byte) float64 {

	var res float64
	switch operator {
		case '+':
			res = n1 + n2
		case '-':
			res = n1 - n2
		case '*':
			res = n1 * n2
		case '/':
			res = n1 / n2
		default:
			fmt.Println("操作符号错误...")
	}
	return res
}