add: loop for statement exercises

13-loops/exercises/07-multiplication-table-exercises/02-math-tables/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: Math Tables
+//
+//  Create division, addition and subtraction tables
+//
+//  1. Get the math operation and
+//     the size of the table from the user
+//
+//  2. Print the table accordingly
+//
+//  3. Correctly handle the division by zero error
+//
+//
+// BONUS #1
+//
+//  Use strings.IndexAny function to detect
+//    the valid operations.
+//
+//  Search on Google for: golang pkg strings IndexAny
+//
+// BONUS #2
+//
+//  Add remainder operation as well (remainder table using %).
+//
+//
+// EXPECTED OUTPUT
+//
+//  go run main.go
+//    Usage: [op=*/+-] [size]
+//
+//  go run main.go "*"
+//    Size is missing
+//    Usage: [op=*/+-] [size]
+//
+//  go run main.go "%" 4
+//    Invalid operator.
+//    Valid ops one of: */+-
+//
+//  go run main.go "*" 4
+//    *    0    1    2    3    4
+//    0    0    0    0    0    0
+//    1    0    1    2    3    4
+//    2    0    2    4    6    8
+//    3    0    3    6    9   12
+//    4    0    4    8   12   16
+//
+//  go run main.go "/" 4
+//    /    0    1    2    3    4
+//    0    0    0    0    0    0
+//    1    0    1    0    0    0
+//    2    0    2    1    0    0
+//    3    0    3    1    1    0
+//    4    0    4    2    1    1
+//
+//  go run main.go "+" 4
+//    +    0    1    2    3    4
+//    0    0    1    2    3    4
+//    1    1    2    3    4    5
+//    2    2    3    4    5    6
+//    3    3    4    5    6    7
+//    4    4    5    6    7    8
+//
+//  go run main.go "-" 4
+//    -    0    1    2    3    4
+//    0    0   -1   -2   -3   -4
+//    1    1    0   -1   -2   -3
+//    2    2    1    0   -1   -2
+//    3    3    2    1    0   -1
+//    4    4    3    2    1    0
+//
+// BONUS:
+//
+//  go run main.go "%" 4
+//    %    0    1    2    3    4
+//    0    0    0    0    0    0
+//    1    0    0    1    1    1
+//    2    0    0    0    2    2
+//    3    0    0    1    0    3
+//    4    0    0    0    1    0
+// ---------------------------------------------------------
+
+func main() {
+}

13-loops/exercises/07-multiplication-table-exercises/02-math-tables/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"
+	"strings"
+)
+
+const (
+	validOps = "%*/+-"
+
+	usageMsg       = "Usage: [op=" + validOps + "] [size]"
+	sizeMissingMsg = "Size is missing"
+	invalidOpMsg   = `Invalid operator.
+Valid ops one of: ` + validOps
+
+	invalidOp = -1
+)
+
+func main() {
+	args := os.Args[1:]
+
+	switch l := len(args); {
+	case l == 1:
+		fmt.Println(sizeMissingMsg)
+		fallthrough
+	case l < 1:
+		fmt.Println(usageMsg)
+		return
+	}
+
+	op := args[0]
+	if strings.IndexAny(op, validOps) == invalidOp {
+		fmt.Println(invalidOpMsg)
+		return
+	}
+
+	size, err := strconv.Atoi(args[1])
+	if err != nil || size <= 0 {
+		fmt.Println("Wrong size")
+		return
+	}
+
+	fmt.Printf("%5s", op)
+	for i := 0; i <= size; i++ {
+		fmt.Printf("%5d", i)
+	}
+	fmt.Println()
+
+	for i := 0; i <= size; i++ {
+		fmt.Printf("%5d", i)
+
+		for j := 0; j <= size; j++ {
+			var res int
+
+			switch op {
+			case "*":
+				res = i * j
+			case "%":
+				if j != 0 {
+					res = i % j
+				}
+			case "/":
+				if j != 0 {
+					res = i / j
+				}
+			case "+":
+				res = i + j
+			case "-":
+				res = i - j
+			}
+
+			fmt.Printf("%5d", res)
+		}
+		fmt.Println()
+	}
+}