Ceaser Cipher

Adriaan

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Previous: Loops Next: Functions

Loops are also a great way to work with String values.

Let's say we wanted to count the number of times the letter "a" appears in a string. We need to look at each character in the string and check if it is an "a".

We can do this using the code below:

let someString = "bhsabbsbabbsjsjabjkojpojpiajihiohsiohigiuygisghiohoah";
let numberOfAs = 0; // we start by setting a variable to hold the a's we count.
for (let i = 0; i < someString.length; i++) {
  // Increase the numberOfAs variable by one of the current character is "a"
  if (someString.charAt(i) == "a") numberOfAs++;
}
console.log("The letter a appears " + numberOfAs + " times.");

Let's say we wanted to modify the string and replace all the a's with *'s. How we can do this?

We'll first need to declare a new empty string to hold the new string. newString = "". We can then iterate over each character in our string and:

If the character is an a, then we add * to our new string
else we add the current character to our new String.

let someString = "bhsabbsbabbsjsjabjkojpojpiajihiohsiohigiuygisghiohoah";
let newString = "";
for (let i = 0; i < someString.length; i++) {
  let currentChar = someString.charAt(i);
  if (currentChar == "a") newString += "*";
  else newString += currentChar;
}
// We can now replace the old string with the new string.
someString = newString;
console.log("Our String is now: " + someString);

Now it's your turn. In the program below, replace all the "a"s with the letter "z", and create a variable named numberOfZs and set that equal to the number of "z"s that apprear in the new String.

Replace a with z

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