added Exercise/Message step to multiplication table exercise

catches wrong solution where `*` is used instead of `x`

Author: spamegg1

core/chapters/c08_nested_loops.py

@@ -416,6 +416,181 @@ def program(self):
             def check(self):
                 return "TypeError: unsupported operand type(s) for +: " in self.result
 
+        class used_times_instead_of_x(ExerciseStep, MessageStep):
+            """
+That's almost correct! Make sure to display the right character `x` in your table.
+For example, your solution should display `3 x 4 = 12` and not `3 * 4 = 12`.
+            """
+
+            def solution(self):
+                for left in range(12):
+                    left += 1
+                    for right in range(12):
+                        right += 1
+                        print(f'{left} * {right} = {left * right}')
+                    print('----------')
+
+            tests = {
+                (): """\
+1 * 1 = 1
+1 * 2 = 2
+1 * 3 = 3
+1 * 4 = 4
+1 * 5 = 5
+1 * 6 = 6
+1 * 7 = 7
+1 * 8 = 8
+1 * 9 = 9
+1 * 10 = 10
+1 * 11 = 11
+1 * 12 = 12
+----------
+2 * 1 = 2
+2 * 2 = 4
+2 * 3 = 6
+2 * 4 = 8
+2 * 5 = 10
+2 * 6 = 12
+2 * 7 = 14
+2 * 8 = 16
+2 * 9 = 18
+2 * 10 = 20
+2 * 11 = 22
+2 * 12 = 24
+----------
+3 * 1 = 3
+3 * 2 = 6
+3 * 3 = 9
+3 * 4 = 12
+3 * 5 = 15
+3 * 6 = 18
+3 * 7 = 21
+3 * 8 = 24
+3 * 9 = 27
+3 * 10 = 30
+3 * 11 = 33
+3 * 12 = 36
+----------
+4 * 1 = 4
+4 * 2 = 8
+4 * 3 = 12
+4 * 4 = 16
+4 * 5 = 20
+4 * 6 = 24
+4 * 7 = 28
+4 * 8 = 32
+4 * 9 = 36
+4 * 10 = 40
+4 * 11 = 44
+4 * 12 = 48
+----------
+5 * 1 = 5
+5 * 2 = 10
+5 * 3 = 15
+5 * 4 = 20
+5 * 5 = 25
+5 * 6 = 30
+5 * 7 = 35
+5 * 8 = 40
+5 * 9 = 45
+5 * 10 = 50
+5 * 11 = 55
+5 * 12 = 60
+----------
+6 * 1 = 6
+6 * 2 = 12
+6 * 3 = 18
+6 * 4 = 24
+6 * 5 = 30
+6 * 6 = 36
+6 * 7 = 42
+6 * 8 = 48
+6 * 9 = 54
+6 * 10 = 60
+6 * 11 = 66
+6 * 12 = 72
+----------
+7 * 1 = 7
+7 * 2 = 14
+7 * 3 = 21
+7 * 4 = 28
+7 * 5 = 35
+7 * 6 = 42
+7 * 7 = 49
+7 * 8 = 56
+7 * 9 = 63
+7 * 10 = 70
+7 * 11 = 77
+7 * 12 = 84
+----------
+8 * 1 = 8
+8 * 2 = 16
+8 * 3 = 24
+8 * 4 = 32
+8 * 5 = 40
+8 * 6 = 48
+8 * 7 = 56
+8 * 8 = 64
+8 * 9 = 72
+8 * 10 = 80
+8 * 11 = 88
+8 * 12 = 96
+----------
+9 * 1 = 9
+9 * 2 = 18
+9 * 3 = 27
+9 * 4 = 36
+9 * 5 = 45
+9 * 6 = 54
+9 * 7 = 63
+9 * 8 = 72
+9 * 9 = 81
+9 * 10 = 90
+9 * 11 = 99
+9 * 12 = 108
+----------
+10 * 1 = 10
+10 * 2 = 20
+10 * 3 = 30
+10 * 4 = 40
+10 * 5 = 50
+10 * 6 = 60
+10 * 7 = 70
+10 * 8 = 80
+10 * 9 = 90
+10 * 10 = 100
+10 * 11 = 110
+10 * 12 = 120
+----------
+11 * 1 = 11
+11 * 2 = 22
+11 * 3 = 33
+11 * 4 = 44
+11 * 5 = 55
+11 * 6 = 66
+11 * 7 = 77
+11 * 8 = 88
+11 * 9 = 99
+11 * 10 = 110
+11 * 11 = 121
+11 * 12 = 132
+----------
+12 * 1 = 12
+12 * 2 = 24
+12 * 3 = 36
+12 * 4 = 48
+12 * 5 = 60
+12 * 6 = 72
+12 * 7 = 84
+12 * 8 = 96
+12 * 9 = 108
+12 * 10 = 120
+12 * 11 = 132
+12 * 12 = 144
+----------
+"""
+            }
+
         tests = {
             (): """\
 1 x 1 = 1