Strings in Programming — Programming interactive lesson

What is a String?

A string is a sequence of characters, usually used to represent text such as words or sentences.

Strings are one of the most common data types in programming, and are enclosed in either single quotes 'Hello' or double quotes "Hello" , depending on the language.

Runnable example

name = "Jenny"
print(name)

String Concatenation

You can combine (concatenate) strings using the + operator.

first = "Hello"
last = "World"
message = first + " " + last
print(message)

const first = "Hello";
const last = "World";
const message = first + " " + last;
console.log(message);

String first = "Hello";
String last = "World";
String message = first + " " + last;
System.out.println(message);

string first = "Hello";
string last = "World";
string message = first + " " + last;
cout << message;

String Length

You can find out how many characters are in a string by using a built-in function or property.

txt = "Hello"
print(len(txt))

const txt = "Hello";
console.log(txt.length);

String txt = "Hello";
System.out.println(txt.length());

string txt = "Hello";
cout << txt.length();

Accessing Characters

Strings are like arrays of characters, so you can access a single character using an index (starting from 0).

txt = "Hello"
print(txt[1]) # prints 'e'

const txt = "Hello";
console.log(txt[1]); // prints 'e'

String txt = "Hello";
System.out.println(txt.charAt(1)); // prints 'e'

string txt = "Hello";
cout << txt[1]; // prints 'e'

Common String Operations

Some of the most common things we do with strings are:

Convert to uppercase or lowercase
Check if a string contains another string
Replace text inside a string

txt = "Hello World"
print(txt.upper()) # HELLO WORLD
print(txt.lower()) # hello world
print("World" in txt) # True
print(txt.replace("World", "Python"))

const txt = "Hello World";
console.log(txt.toUpperCase()); // HELLO WORLD
console.log(txt.toLowerCase()); // hello world
console.log(txt.includes("World")); // true
console.log(txt.replace("World", "JavaScript"));

String txt = "Hello World";
System.out.println(txt.toUpperCase()); // HELLO WORLD
System.out.println(txt.toLowerCase()); // hello world
System.out.println(txt.contains("World")); // true
System.out.println(txt.replace("World", "Java")); // Hello Java

#include <iostream>
#include <string>
#include <algorithm> // for transform
#include <cctype> // for toupper, tolower
using namespace std;
int main() {
 string txt = "Hello World";
 // Convert to uppercase
 string upper_txt = txt;
 transform(upper_txt.begin(), upper_txt.end(), upper_txt.begin(), ::toupper);
 cout << upper_txt << endl; // HELLO WORLD
 // Convert to lowercase
 string lower_txt = txt;
 transform(lower_txt.begin(), lower_txt.end(), lower_txt.begin(), ::tolower);
 cout << lower_txt << endl; // hello world
 // Check if string contains "World"
 if (txt.find("World") != string::npos) {
 cout << "true" << endl; // true
 } else {
 cout << "false" << endl;
 }
 // Replace "World" with "C++"
 string replaced_txt = txt;
 size_t pos = replaced_txt.find("World");
 if (pos != string::npos) {
 replaced_txt.replace(pos, 5, "C++");
 }
 cout << replaced_txt << endl; // Hello C++
 return 0;
}

Note

Each programming language has its own set of string functions. The most common operations like finding length, accessing characters, and replacing text exist in almost all languages.

Real-Life Example

Strings are especially useful when working with user input. For example, let's say we are creating a program to greet the user by name:

name = "Jenny"
greeting = "Hello, " + name + "!"
print(greeting)

const name = "Jenny";
const greeting = "Hello, " + name + "!";
console.log(greeting);

String name = "Jenny";
String greeting = "Hello, " + name + "!";
System.out.println(greeting);

string name = "Jenny";
string greeting = "Hello, " + name + "!";
cout << greeting;