diff --git a/src/main.nim b/src/main.nim
index 7d26e60..4c44993 100644
--- a/src/main.nim
+++ b/src/main.nim
@@ -1,8 +1,7 @@
-import strutils, sequtils, os, procedures, strformat
-# TODO: while loop to check if inputs are valid
+import strutils, sequtils, os, procedures
 
 var operation: string
-# if command is "dot" or "cross" preform that operation
+#? if command is "dot" or "cross" preform that operation
 if paramStr(0).endsWith("/dot") or paramStr(0) == "dot":
     operation = "dot"
     echo "Calculating the dot product:"
@@ -11,9 +10,16 @@ elif paramStr(0).endsWith("/cross") or paramStr(0) == "cross":
     echo "Calculating the cross product:"
 else:
     echo "Would you like to preform the dot or cross product?"
-    operation = readLine(stdin)
+    operation = toLowerAscii(readLine(stdin))
+    case operation:
+        of "dot":
+            operation = "dot"
+        of "cross":
+            operation = "cross"
+        else:
+            quit "Invalid matrix operation!", QuitFailure
 
-# record first matrix
+#? record first matrix
 echo "Enter number of rows in the first matrix:"
 let r1: int = parseInt(readLine(stdin)) 
 echo "Enter number of columns in the first matrix:"
@@ -23,7 +29,7 @@ procedures.fillMatrix(m1, r1, c1)
 
 echo ""
 
-# record second matrix
+#? record second matrix
 echo "Enter number of rows in the second matrix:"
 let r2: int = parseInt(readLine(stdin))
 echo "Enter number of columns in the second matrix:"
@@ -31,12 +37,12 @@ let c2: int = parseInt(readLine(stdin))
 var m2 = newSeqWith(r2, newSeq[float](c2))
 procedures.fillMatrix(m2, r2, c2)
 
-# resultent matrix
+#? resultent matrix
 var m = newSeqWith(0, newSeq[float](0))
 
 case operation:
     of "dot":
-        m = dot(m1, m2)  # calculate dot product (in procedures)
+        m = dot(m1, m2)  #? calculate dot product (in procedures)
     of "cross":
         echo "*do cross product*" # TODO: calculate cross product (in procedures)
     else: