Introduction to Strings

You already use strings every single day. Your name. A WhatsApp message. A YouTube search. A password. All of these are just text. In programming we call this text a string. So before you can build anything real, you need to understand how the computer holds your words. That is what this lesson is about.

📚 What Is a String?

A string is a sequence of characters placed one after another, like a word or a sentence.

A character is one single symbol. The letter A is a character. The digit 7 is a character. Even a space is a character. When you line up many characters in order, you get a string.

So "Riya" is a string made of four characters: R, i, y, a.

Here is an easy way to picture it. Think of a string like beads on a thread. Each bead is one character. The thread keeps them in order. Pull the thread and the word stays as Riya, not yaRi. So order matters in a string.

🧠 How a String Is Stored Inside the Computer

Now the interesting part. The computer does not actually store letters. It only stores numbers. So how does it keep your name?

The trick is simple. Every character is given a number. The computer agreed on a shared table that maps each character to a number. This table is called ASCII, which stands for American Standard Code for Information Interchange. It is just a lookup list. For example A is 65, B is 66, and a small a is 97. Even a space has a number, and that number is 32.

So when you store "Hi", the computer is really storing the numbers 72 and 105, sitting next to each other in memory.

Let us see the word Hi the way the computer sees it.

A string is laid out in memory just like a character array. The characters sit in neighboring boxes, in order, and each box holds one number.

Let us actually print the number behind a character so you believe it. The code below takes the letter A and shows the number the computer stores for it.

#include <stdio.h>

// Print the ASCII number behind a character
void showCode(char ch) {
    // %d prints the character as its number
    printf("The character '%c' is stored as %d\n", ch, ch);
}

int main(void) {
    showCode('A');
    return 0;
}

The character 'A' is stored as 65

#include <iostream>
using namespace std;

// Print the ASCII number behind a character
void showCode(char ch) {
    // (int)ch turns the character into its number
    cout << "The character '" << ch << "' is stored as " << (int)ch << endl;
}

int main() {
    showCode('A');
    return 0;
}

The character 'A' is stored as 65

public class CharCode {
    // Print the ASCII number behind a character
    static void showCode(char ch) {
        // (int) ch turns the character into its number
        System.out.println("The character '" + ch + "' is stored as " + (int) ch);
    }

    public static void main(String[] args) {
        showCode('A');
    }
}

The character 'A' is stored as 65

# Print the ASCII number behind a character
def show_code(ch):
    # ord() gives the number for a character
    print(f"The character '{ch}' is stored as {ord(ch)}")

show_code('A')

The character 'A' is stored as 65

// Print the ASCII number behind a character
function showCode(ch) {
  // charCodeAt(0) gives the number for the character
  console.log(`The character '${ch}' is stored as ${ch.charCodeAt(0)}`);
}

showCode("A");

The character 'A' is stored as 65

See, the same letter A gives 65 in every language. That is because the ASCII table is shared by all of them.

✍️ Creating and Printing a String

Now let us make a real string, print it, and also find how long it is.

The length of a string is just the count of characters in it. The word Hello has 5 characters, so its length is 5.

Here is the same task in all five languages. We create the string Hello, print it, then print its length.

#include <stdio.h>
#include <string.h>

int main(void) {
    // In C a string is an array of characters
    char greeting[] = "Hello";

    printf("The string is: %s\n", greeting);
    // strlen counts the characters
    printf("Its length is: %zu\n", strlen(greeting));
    return 0;
}

The string is: Hello
Its length is: 5

#include <iostream>
#include <string>
using namespace std;

int main() {
    // Create a string
    string greeting = "Hello";

    cout << "The string is: " << greeting << endl;
    // .length() counts the characters
    cout << "Its length is: " << greeting.length() << endl;
    return 0;
}

The string is: Hello
Its length is: 5

public class MakeString {
    public static void main(String[] args) {
        // Create a string
        String greeting = "Hello";

        System.out.println("The string is: " + greeting);
        // .length() counts the characters
        System.out.println("Its length is: " + greeting.length());
    }
}

The string is: Hello
Its length is: 5

# Create a string
greeting = "Hello"

print("The string is:", greeting)
# len() counts the characters
print("Its length is:", len(greeting))

The string is: Hello
Its length is: 5

// Create a string
const greeting = "Hello";

console.log("The string is:", greeting);
// .length counts the characters
console.log("Its length is:", greeting.length);

The string is: Hello
Its length is: 5

The words for “create” and “length” change a little in each language. But the idea is exactly the same everywhere. You give the text a name. You print it. Then you ask how many characters it holds.

🔢 Picking One Character: Indexing

Often you do not want the whole string. You want just one character from it. Maybe the first letter of a name. Maybe the last digit of a code. For that we use the index.

The index is the position number of a character inside the string. And here is the part that surprises every beginner. Counting starts at 0, not 1.

So in Hello the positions look like this.

So index 0 is H, the very first character. Index 4 is o, the last one. To reach a character you write the string name and then the index in square brackets, like greeting[0].

The code below grabs the character at index 0 from Hello.

#include <stdio.h>

int main(void) {
    char greeting[] = "Hello";

    // Square brackets reach one character by its index
    printf("First character: %c\n", greeting[0]);
    return 0;
}

First character: H

#include <iostream>
#include <string>
using namespace std;

int main() {
    string greeting = "Hello";

    // Square brackets reach one character by its index
    cout << "First character: " << greeting[0] << endl;
    return 0;
}

First character: H

public class IndexString {
    public static void main(String[] args) {
        String greeting = "Hello";

        // charAt reaches one character by its index
        System.out.println("First character: " + greeting.charAt(0));
    }
}

First character: H

greeting = "Hello"

# Square brackets reach one character by its index
print("First character:", greeting[0])

First character: H

const greeting = "Hello";

// Square brackets reach one character by its index
console.log("First character:", greeting[0]);

First character: H

⚠️ Common Mistakes Beginners Make

A few small things trip up almost everyone at the start. Keep these in mind.

• Forgetting that the index starts at 0. The first character is at index 0, never index 1.
• Counting the quotes as part of the string. "Hi" has 2 characters, not 4. The quotes just mark the start and the end.
• Thinking a space is empty. A space is a real character with its own number, and it adds to the length.
• Mixing up a character and a string. 'A' is one character. "A" is a string that happens to hold one character. Some languages care about this difference a lot.

🧩 What You’ve Learned

✅ A string is a sequence of characters in order, like a word or a sentence.

✅ Inside the computer a string is stored like a character array, with characters sitting next to each other.

✅ Every character is really a number, mapped by the ASCII table, and Unicode extends this to every language and emoji.

✅ You can create a string, print it, and find its length in every language with the same idea.

✅ Indexing reaches one character by its position, and counting always starts at 0.

🚀 What’s Next?

• String Operations
• Mutable vs Immutable Strings