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Haskell Program to create Case statement
In Haskell, we can use pattern matching, digitToInt, reads and a user-defined functions to convert char-type variables to int. In the first example, we are going to use cases for matching the pattern and in the second example, we are going to use (charToInt c = if isDigit c then Just (digitToInt c) else Nothing). And in third example, we are going to use (charToInt c = case reads [c] of [(x, "")] -> Just x and _ -> Nothing) function.
Algorithm
Step 1 − The internal function is defined
Step 2 − Program execution will be started from main function. The main() function has whole control of the program. It is written as main = do.
Step 3 − The variable named, “digit” is being initialized. It will hold the character that is to be converted to respective Integer number.
Step 4 − The cases are defined for comparing the digits.
Step 5 − The resultant Integer value is printed to the console using ‘putStrLn’ statement after the function is called.
Example 1
In this example, the function is defined using user-defined charToInt function with the help of fromEnum function to convert the char type variables to Int.
charToInt :: Char -> Int
charToInt c = fromEnum c - fromEnum '0'
main :: IO ()
main = do
let digit = '4'
case digit of
'0' -> putStrLn "The integer value is 0."
'1' -> putStrLn "The integer value is 1."
'2' -> putStrLn "The integer value is 2."
'3' -> putStrLn "The integer value is 3."
'4' -> putStrLn "The integer value is 4."
'5' -> putStrLn "The integer value is 5."
'6' -> putStrLn "The integer value is 6."
'7' -> putStrLn "The integer value is 7."
'8' -> putStrLn "The integer value is 8."
'9' -> putStrLn "The integer value is 9."
_ -> putStrLn "Invalid input. Please enter a digit character."
Output
The integer value is 4.
Example 2
In this example, the function is defined using user-defined charToInt function with the help of digitToInt and isDigit function to convert the char type variables to Int.
import Data.Char (digitToInt, isDigit)
charToInt :: Char -> Maybe Int
charToInt c = if isDigit c then Just (digitToInt c) else Nothing
main :: IO ()
main = do
let digit = '6'
case charToInt digit of
Just x -> putStrLn $ "The integer value is " ++ show x ++ "."
Nothing -> putStrLn "Invalid input. Please enter a digit character."
Output
The integer value is 6.
Example 3
In this example, the function is defined using user-defined charToInt function with the help of reads function to convert the char type variables to Int.
import Data.Char (digitToInt)
charToInt :: Char -> Maybe Int
charToInt c = case reads [c] of
[(x, "")] -> Just x
_ -> Nothing
main :: IO ()
main = do
let digit = '5'
case charToInt digit of
Just x -> putStrLn $ "The integer value is " ++ show x ++ "."
Nothing -> putStrLn "Invalid input. Please enter a digit character."
Output
The integer value is 5.
Conclusion
The conversion of a char variable to an int variable typically involves extracting the integer value of the character from its character encoding. This can be done using built-in functions provided by the programming language, or by implementing a custom function to extract the integer value from the character encoding. In Haskell, a char type variables is converted to int using user-defined function along with pattern matching, digitToInt and reads functions.
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