add: for statement loop exercises

13-loops/exercises/03-sum-up-to-n/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+// ---------------------------------------------------------
+// EXERCISE: Sum up to N
+//
+//  1. Get two numbers from the command-line: min and max
+//  2. Convert them to integers (using Atoi)
+//  3. By using a loop, sum the numbers between min and max
+//
+// RESTRICTIONS
+//  1. Be sure to handle the errors. So, if a user doesn't
+//     pass enough arguments or she passes non-numerics,
+//     then warn the user and exit from the program.
+//
+//  2. Also, check that, min < max.
+//
+// HINT
+//  For converting the numbers, you can use `strconv.Atoi`.
+//
+// EXPECTED OUTPUT
+//  Let's suppose that the user runs it like this:
+//
+//    go run main.go 1 10
+//
+//  Then it should print:
+//
+//    1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 = 55
+// ---------------------------------------------------------
+
+func main() {
+}

13-loops/exercises/03-sum-up-to-n/solution/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+)
+
+func main() {
+	if len(os.Args) < 3 {
+		fmt.Println("gimme two numbers")
+		return
+	}
+
+	min, err1 := strconv.Atoi(os.Args[1])
+	max, err2 := strconv.Atoi(os.Args[2])
+	if err1 != nil || err2 != nil || min >= max {
+		fmt.Println("wrong numbers")
+		return
+	}
+
+	var sum int
+	for i := min; i <= max; i++ {
+		sum += i
+
+		fmt.Print(i)
+		if i != max {
+			fmt.Print(" + ")
+		}
+	}
+	fmt.Printf(" = %d\n", sum)
+}