Golang for loop-CodePudding

package main

import "fmt"

func main() {
   num := []int{}
   fmt.Println(num)
   for i := 1; i <= 64; i   {
      if i == 1 {
        num = append(num, i)
      } else if i == 2 {
        num = append(num, i)
      } else if i == 3 {
        num = append(num, 4)
      } else {
        num = append(num, 2*(num[len(num)-1]))
            // get last item
    }
}
for _, s := range num {
    fmt.Println(s)
}
}

I'm beginner level on golang and tried to make a for loop as above. Actually I just wanted to solve that famous chess board and wheat question. You can see the url below. But on the last item it gives a negative result if i=64. I just couldn't figure it out why it is negative. Can you help me please, thank you in advance.

https://en.m.wikipedia.org/wiki/Wheat_and_chessboard_problem

CodePudding user response：

because the last number 9223372036854775808 is out bound of int64, https://pkg.go.dev/builtin#int64

change to uint64 works.

package main

import "fmt"

func main() {
    num := []uint64{}
    fmt.Println(num)
    for i := 1; i <= 64; i   {
        if i == 1 {
            num = append(num, uint64(i))
        } else if i == 2 {
            num = append(num, uint64(i))
        } else if i == 3 {
            num = append(num, uint64(4))
        } else {
            num = append(num, 2*(num[len(num)-1]))
            // get last item
        }
    }
    for _, s := range num {
        fmt.Println(s)
    }
}

gives

[]
1
2
4
8
16
32
64
128
256
512
1024
2048
4096
8192
16384
32768
65536
131072
262144
524288
1048576
2097152
4194304
8388608
16777216
33554432
67108864
134217728
268435456
536870912
1073741824
2147483648
4294967296
8589934592
17179869184
34359738368
68719476736
137438953472
274877906944
549755813888
1099511627776
2199023255552
4398046511104
8796093022208
17592186044416
35184372088832
70368744177664
140737488355328
281474976710656
562949953421312
1125899906842624
2251799813685248
4503599627370496
9007199254740992
18014398509481984
36028797018963968
72057594037927936
144115188075855872
288230376151711744
576460752303423488
1152921504606846976
2305843009213693952
4611686018427387904
9223372036854775808