Add code

3-map-in-go/Makefile

@@ -0,0 +1,2 @@
+all:
+	go run main.go

3-map-in-go/main.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+    "fmt"
+)
+
+func main() {
+    var a [10]int
+
+    for i := range a {
+        a[i] = i
+    }
+
+    var b [10]struct{n int; nn int}
+
+    for i, n := range a {
+        b[i].n  = n
+        b[i].nn = n * n
+    }
+
+    for _, v := range b {
+        fmt.Printf("%v: %v\n", v.n, v.nn)
+    }
+}