【golang】有无大佬帮忙看下这个代码为什么不行，自测没问题，一提交全红www

package main
import(
    "fmt"
)
func main(){
    var(
        str [50]byte
        n int
    )
    fmt.Scanf("%d",&n)
    for i := 0;str[i] != '\n';i ++{
        fmt.Scanf("%c",&str[i])
        if str[i] == '\n'{
            break
        }
        for j := 0;j < n;j ++{
            if str[i] != 'z'{
                str[i] = str[i] + 1
            }else{
                str[i] = 'a'
            }
        }
    }
    for i := 0;i < len(str);i ++{
        fmt.Printf("%c",str[i])
    }
    fmt.Printf("\n")
}