Convert rune to int?

why don't you do only "string(rune)".

s:="12345678910"
var factor,sum int
for i,x:=range s{
    if i%2==0{
            factor=1
        }else{
        factor=3
    }
        xstr:=string(x) //x is rune converted to string
        xint,_:=strconv.Atoi(xstr)
        sum+=xint*factor
}
fmt.Println(sum)

The problem is simpler than it looks. You convert a rune value to an int value with int(r). But your code implies you want the integer value out of the ASCII (or UTF-8) representation of the digit, which you can trivially get with r - '0' as a rune, or int(r - '0') as an int. Be aware that out-of-range runes will corrupt that logic.

For example, sum += (int(c) - '0') * factor,

package main

import (
    "fmt"
    "strconv"
    "unicode/utf8"
)

func main() {
    s := "9780486653556"
    var factor, sum1, sum2 int
    for i, c := range s[:12] {
        if i%2 == 0 {
            factor = 1
        } else {
            factor = 3
        }
        buf := make([]byte, 1)
        _ = utf8.EncodeRune(buf, c)
        value, _ := strconv.Atoi(string(buf))
        sum1 += value * factor
        sum2 += (int(c) - '0') * factor
    }
    fmt.Println(sum1, sum2)
}

Output:

124 124