Lære Challenge: Accessing and Manipulating String Elements

Indexing a string

We can access the elements of a string (which are essentially char characters) using square bracket [] indexing, similar to arrays. This also allows us to replace a character at a specific position.

indexing.h


              12
            
string str = "Cpdefinity"; // Cpdefinity
str[1] = 'o'; // Codefinity

Note

Indexing in a string starts from zero, just like in arrays.

The length of the string

With that indexing, you can try to access a wrong index (that is out of range), and the compiler will tell you nothing about that.

main.cpp


              1234567
            
#include <iostream>

int main()
{
    std::string word = "Codefinity";
    std::cout << word[12]; // Word's length is 10
}

As you can see, the output is unexpected, and C++ does not provide a warning about the issue. To prevent this, you can use the .length() method to determine the length of a string and ensure the index is within the valid range.

main.cpp


              123456789101112
            
#include <iostream>

int main()
{
    std::string word = "Codefinity";
    int index = 12;
    
    if (index >= word.length()) 
	    std::cout << "The output is unexpected!" << std::endl;
    else
        std::cout << word[index]; // Word's length is 10
}

Indexing using method

Another way of indexing is using the .at() method. To get the character with index n, we can use the following syntax:

at.h


              1
            
str.at(n);

It works the same as str[n] but will raise an error if you specify an index that is out of range.

main.cpp


              12345678
            
#include <iostream>

int main()
{
    std::string word = "Codefinity";
    std::cout << word.at(12); // word's length is 10
    // Try outputting the character with the index 5
}

Practice

As was said before, we can replace the characters inside a string using indexing (both with [] and .at()). Here is an example:

main.cpp


              123456789
            
#include <iostream>

int main()
{
    std::string word = "Cpdefinitu";
    word[1] = 'o';
    word.at(word.length() - 1) = 'y'; // length - 1 accesses the last element
    std::cout << word;
}

Opgave

Swipe to start coding

You have an email address as a string. Your task is to mask the username part of the email for privacy.

The function maskEmail takes a string representing the email address.

Inside maskEmail, use the find method to locate the position of the '@' symbol, which marks the end of the username.
Check if the username is longer than 1 character. If not, return the email unchanged.
Use a for loop to iterate from index 1 up to (but not including) the position of '@'.
Within the loop, replace each character with '*' to mask the username.
Return the modified email.

Example

"alex@example.com" => "a***@example.com"
"bob@example.com" => "b**@example.com"
"x@domain.com" => "x@domain.com"

Løsning

solution.cpp

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Sektion 3. Kapitel 3

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Suggested prompts:

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Indexing a string

indexing.h


              12
            
string str = "Cpdefinity"; // Cpdefinity
str[1] = 'o'; // Codefinity

Note

Indexing in a string starts from zero, just like in arrays.

The length of the string

With that indexing, you can try to access a wrong index (that is out of range), and the compiler will tell you nothing about that.

main.cpp


              1234567
            
#include <iostream>

int main()
{
    std::string word = "Codefinity";
    std::cout << word[12]; // Word's length is 10
}

main.cpp


              123456789101112
            
#include <iostream>

int main()
{
    std::string word = "Codefinity";
    int index = 12;
    
    if (index >= word.length()) 
	    std::cout << "The output is unexpected!" << std::endl;
    else
        std::cout << word[index]; // Word's length is 10
}

Indexing using method

Another way of indexing is using the .at() method. To get the character with index n, we can use the following syntax:

at.h


              1
            
str.at(n);

It works the same as str[n] but will raise an error if you specify an index that is out of range.

main.cpp


              12345678
            
#include <iostream>

int main()
{
    std::string word = "Codefinity";
    std::cout << word.at(12); // word's length is 10
    // Try outputting the character with the index 5
}

Practice

As was said before, we can replace the characters inside a string using indexing (both with [] and .at()). Here is an example:

main.cpp


              123456789
            
#include <iostream>

int main()
{
    std::string word = "Cpdefinitu";
    word[1] = 'o';
    word.at(word.length() - 1) = 'y'; // length - 1 accesses the last element
    std::cout << word;
}

Opgave

Swipe to start coding

You have an email address as a string. Your task is to mask the username part of the email for privacy.

The function maskEmail takes a string representing the email address.

Inside maskEmail, use the find method to locate the position of the '@' symbol, which marks the end of the username.
Check if the username is longer than 1 character. If not, return the email unchanged.
Use a for loop to iterate from index 1 up to (but not including) the position of '@'.
Within the loop, replace each character with '*' to mask the username.
Return the modified email.

Example

"alex@example.com" => "a***@example.com"
"bob@example.com" => "b**@example.com"
"x@domain.com" => "x@domain.com"

Løsning

solution.cpp

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Var alt klart?

Tak for dine kommentarer!

Sektion 3. Kapitel 3

single