refactoring: clarifications in operation handler methods

src/operationHandler.c

@@ -4,6 +4,7 @@
 #include <stdlib.h>
 #include <string.h>
 
+// checking integer input as operation id
 bool checkOperationInput(int input) {
     switch (input) {
         case 4: case 3: case 2: case 1:
@@ -12,9 +13,12 @@ bool checkOperationInput(int input) {
     return false;
 }
 
+// full input process
 int* evaluateInput(char* input, int operation) {
+    // check if formatting is correct
     if(!containsTwoNumbers(input)) return NULL;
     int firstNumber = extractFirstNumber(input);
+    // origin string "input" has been edited
     int secondNumber = atoi(input);
     int* result = malloc(sizeof(int));
     switch (operation) {