feat: P-1.31 completed and commented

lab-3_4/P-1.31.py

@@ -5,3 +5,59 @@ coin to give back as change for the difference between the amount given and the
 to the bills and coins can be based on the monetary system of any current or former government. Try to design your
 program so that it returns as few bills and coins as possible.
 """
+
+# global var, dict of all possible US currency denominations converted to cents
+denominations = {
+    "hundred-dollar bill(s)": 10000,
+    "fifty-dollar bill(s)": 5000,
+    "twenty-dollar bill(s)": 2000,
+    "ten-dollar bill(s)": 1000,
+    "five-dollar bill(s)": 500,
+    "one-dollar bill(s)": 100,
+    "quarter(s)": 25,
+    "dime(s)": 10,
+    "nickel(s)": 5,
+    "penny(ies)": 1,
+}
+
+
+def make_change():
+    # input validation block
+    while True:
+        # try that both vars are formatted correctly and converted to cents
+        try:
+            charged = round(float(input("Enter a dollar amount to be charged: ")) * 100)
+            given = round(
+                float(input("Enter a dollar amount for the amount given: ")) * 100
+            )
+            # print error message if not enough given
+            if given < charged:
+                print("Pay up.")
+            # print error message if a negative amount or 0 is entered
+            elif charged <= 0:
+                print("Please enter a positive dollar amount")
+            else:
+                break
+        # handle ValueError if non-numeric input given
+        except ValueError:
+            print("Please only enter dollar amounts")
+    # calculate change and store it in 'total_change' for printing
+    change = given - charged
+    total_change = change
+    # print message if no change is needed
+    if change == 0:
+        print("No change due.")
+    # iterate over the pre-defined dict and split into names and values
+    for name, value in denominations.items():
+        # store how many of each denomination is needed to make change of the remainder
+        count = change // value
+        # set 'change' as the remainder left after change is issued
+        change = change % value
+        # if there was at least 1 of a denomination given, print how many and its name
+        if count > 0:
+            print(f"{count}", name)
+    # print total change recalculation in dollars
+    print(f"Total change is ${total_change / 100:.2f}")
+
+
+make_change()