Strings are a sequence of zero or more characters written inside quotes used to represent text.

Strings may consist of letters, numbers, symbols, words, or sentences.

Strings are immutable, they cannot be changed.

Each character in a string has an index.

The first character will be index 0 the second character will be index 1 and so on.

There are two ways to access an individual character in a string.

charAt() method

const str1 = "abc"; string

str1.charAt(0); character at index 0 → "a"

str1.charAt(1); character at index 1 → "b"

str1.charAt(2); character at index 2 → "c"

str1.charAt(3); character at index 3 → "" index not found

Alternatively use at() or slice() methods

bracket notation []

const str2 = "abc"; string

str2[0]; character at index 0 → "a"

str2[1]; character at index 1 → "b"

str2[2]; character at index 2 → "c"

str2[3]; character at index 3 → undefined index not found

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Case sensitivity defines whether uppercase and lowercase letters are treated as distinct or equivalent.

case-sensitive will distinguish between uppercase and lowercase letters.

"A" will be treated as distinct to the letter "a" and vice versa. They will be treated as different.

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Numbers are used to represent both integer and floating-point values.

Numbers are most commonly expressed in literal forms like 255 or 3.14159 ↴

let num1 = 5; → number

let num2 = 2.5; → number

let num3 = num1 + num2;

console.log(num3); returns ↴

7.5 → number

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Count occurrences of a character in a string using a for loop

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for loop repeatedly executes a block of code until a specified condition evaluates to false.

The loop runs a block of code a set number of times, defined by an initialization, a condition, and an increment.

for (let x = 0; x < 4; x++) {

console.log(x);

}

Loop variable x is initialized to 0

Condition x < 4 is checked before each iteration.

The loop will continue to run as long as x is less than 4

The loop repeatedly executes a block of code 4 times, from 0 to 3

For each iteration of the loop, the current value of x is printed to the console.

After each iteration, x is incremented by 1 x++

When x reaches 4 the condition evaluates to false, terminating the loop.

0

1

2

3 → printed to console

The loop will iterate through each character in the string.

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Initialize a variable to hold the string to be searched.

const string1 = "HELLO WORLD, hello world"; → user input

Initialize a variable to hold the character to count.

const char1 = "o"; → user input

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Define a function countOccurrences to count occurrences of a character in a string.

The function takes two parameters ↴

string1 the string to be searched, str

char1 the character to count, char

The function returns the number of occurrences of the specified character found in the string.

Initialize a counter to zero to count occurrences of char

let count = 0 count

Loop through each character in str

for (let x = 0; x < str.length; x++) {}

If current character str[x] matches char

if (str[x] === char)

Increment counter by 1

count++

After the loop completes return the count.

return count

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Call the function with ↴

countOccurrences(string1, char1);

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Count occurrences of the character "o" in a string | case-sensitive