Question

Hi, trying to make a converter but is running into an issue of displaying an error message (at the bottom of the program) when currencies are entered incorrectly. I was suggested after adding result = 0, I should test for result == 0. With only making necessary changes can you explain what this means to my program and how?

result = 0
money = float(input("Please enter the From amount to be converted: "))
fromCurrency = input("Please enter the From currency (USD, EUR, or JYP): ")
toCurrency = input("Please enter the To currency (USD, EUR, or JYP): ")

## conversions taken as of 9/26/19
# 1 USD = .91 EUR (1.1 factor), 1 USD = 107.63 JYP (.00929 factor), 1 EUR = 117.81 JYP (.0084 factor)
usdEur = money / 1.1
eurUsd = money * 1.1
usdJyp = money / .00929
jypUsd = money * .00929
eurJyp = money / .00848
jypEur = money * .00848

# Conversion from USD to other currencies
if fromCurrency.lower() == ("usd"):
if toCurrency.lower() == ("eur"):
result = usdEur
if toCurrency.lower() == ("jyp"):
result = usdJyp
print(money, fromCurrency, "equals", result, toCurrency)

elif fromCurrency.lower() == ("eur"):
if toCurrency.lower() == ("usd"):
result = eurUsd
if toCurrency.lower() == ("jyp"):
result = eurJyp
print(money, fromCurrency, "equals", result, toCurrency)

elif fromCurrency.lower() == ("jyp"):
if toCurrency.lower() == ("usd"):
result = jypUsd
if toCurrency.lower() == ("eur"):
result = jypEur
print(money, fromCurrency, "equals", result, toCurrency)

else: #does not work when 'to' currency is wrong
print("Error! Currency not available for conversion")

Answer 1

Changes made to the program:

1. Removed the print statement for printing result from all if blocks and added at the end of the program. One print is enough instead of three.
2. Added If else condition to check if the result is 0, to print the error message.
3. Also added money!=0 condition for displaying error message. This is required because if money entered is 0, and though both fromCurrency and toCurrency entered are valid, program displays the error message.
4. To avoid above case, added another if condition to check if money==0. If money==0, "Money entered is 0" is printed instead of error message.

Program:

Note: Program is explained using comments in the code.

Code:

#initialise result to 0
result = 0

#input money from user
money = float(input("Please enter the From amount to be converted: "))

#input from currency
fromCurrency = input("Please enter the From currency (USD, EUR, or JYP): ")

#input to currnecy
toCurrency = input("Please enter the To currency (USD, EUR, or JYP): ")

## conversions taken as of 9/26/19
# 1 USD = .91 EUR (1.1 factor), 1 USD = 107.63 JYP (.00929 factor), 1 EUR = 117.81 JYP (.0084 factor)

#If conversion is from USD to EUR
usdEur = money / 1.1

#If conversion is from EUR to USD
eurUsd = money * 1.1

#If conversion is from USD to JYP
usdJyp = money / .00929

#If conversion is from JYP to USD
jypUsd = money * .00929

#If conversion is from EUR to JYP
eurJyp = money / .00848

#If conversion is from JYP to EUR
jypEur = money * .00848

# Conversion from USD to other currencies
if fromCurrency.lower() == ("usd"):
   if toCurrency.lower() == ("eur"):
       result = usdEur
   if toCurrency.lower() == ("jyp"):
       result = usdJyp
# Conversion from EUR to other currencies
elif fromCurrency.lower() == ("eur"):
   if toCurrency.lower() == ("usd"):
       result = eurUsd
   if toCurrency.lower() == ("jyp"):
       result = eurJyp
# Conversion from JYP to other currencies
elif fromCurrency.lower() == ("jyp"):
   if toCurrency.lower() == ("usd"):
       result = jypUsd
   if toCurrency.lower() == ("eur"):
       result = jypEur

#displays error message if any of fromCurrency or toCurrency is invalid

#If any of the fromCurrency or toCurrency is invalid(i.e not USD or EUR or JYP)
#Then the if conditions above wont satisfy and the result will be same as initialised
# that is 0.

# If money entered is 0 then though fromCurrency and toCurrency entered are
# valid result will be 0.

#So the condition to check for displaying error meassage is result==0 AND money!=0
if(result==0 and money!=0):
   print("Error! Currency not available for conversion")
elif(money==0):
   print("Money entered is 0")
else:
   print(money, fromCurrency, "equals", result, toCurrency)

Output: