Exercise: Character operations

stringToUpperCase: Converts each letter in a string to its uppercase version. For example "Hello!" becomes "HELLO!".

stringToLowerCase: The opposite of stringToUpperCase. "Hello!" becomes "hello!".

toggleCase: "Hello!" becomes "hELLO!".

equalIgnoreCase: Returns whether two strings are equal, ignoring case. For example, returns true for "aBc" and "ABC".

isNumber: Returns whether a string consists entirely of digits.

getPositionsInAlphabet: Takes a string and returns an integer array with the position of each letter in the alphabet, starting at zero. If a character in the string is not a letter, returns -1. For example:

'A' → 0
'g' → 6
'z' → 25
'!' → -1

Your program without methods can look like this:

String input = "Hello world!"; System.out.println("Upper case: " + stringToUpperCase(input)); System.out.println("Lower case: " + stringToLowerCase(input)); String toggled = toggleCase(input); System.out.println("Toggled: " + toggled); System.out.println("\"" + input + "\" and \"" + toggled + "\" are " + "equal (ignoring case): " + equalIgnoreCase(input, toggled)); String numberMaybe = "5801"; System.out.println(numberMaybe + " is a number: " + isNumber(numberMaybe)); String letters = "Abc Xyz"; int[] positionsInAlphabet = getPositionsInAlphabet(letters); System.out.println("Positions in alphabet of \"" + letters + "\": " + toString(positionsInAlphabet));

Program output:

Upper case: HELLO WORLD! Lower case: hello world! Toggled: hELLO WORLD! "Hello world!" and "hELLO WORLD!" are equal (ignoring case): True 5801 is a number: True Positions in alphabet of "Abc Xyz": 0, 1, 2, -1, 23, 24, 25

Hints 💡

Consult an ASCII table to see which value is assigned to which character.
Notice that the difference between the values of uppercase "A" (65) and lowercase "a" (97) is 32.
The same is true for uppercase "B" (66) and lowercase "b" (98).
To create a new character by using the ASCII value of an existing character, you can use addition and a type cast:
```
char letter = 'A';
char newLetter = (char)(letter + 1);
// newLetter is now 'B'
```
You can compare characters with integers. For example, to see whether a character c represents a digit (0 - 9):
```
if (c >= 48 && c <= 57)
```

Exercise: Character operations

Hints 💡

Hand in instructions