Lære Challenge: Searching Within Strings

Method find()

Sometimes, you may need to search for specific text within a string. This can be done using the .find() or .rfind() methods. Let’s begin with the .find() method.

find.h


              1
            
str.find("text to find")

It returns the index of the first character of the first match.

main.cpp


              1234567
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.find("code") << std::endl; // (code)codefinity
}

You can also specify the position of the first character in the string to be considered in the search. It can be done using the pos argument. Any characters before the pos index are ignored in a search.

Here is an example of finding the first "code" starting from a 3-rd character.

main.cpp


              1234567
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.find("code", 3) << std::endl; // __de(code)finity
}

Method rfind()

You can also locate the last occurrence of some text using the .rfind() method.

rfind.h


              1
            
str.rfind("text to find")

While .find() retrieves the first occurrence of text, .rfind() finds the last occurrence and stands for reverse find.

main.cpp


              12345678
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.find("code") << std::endl;
    std::cout << str.rfind("code") << std::endl;
}

Note

If no match is found, both .find() and .rfind() return a special value, string::npos. This value represents no position and indicates that the search was unsuccessful.

main.cpp


              12345678
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.rfind("abc") << std::endl;
    std::cout << std::string::npos << std::endl;
}

Opgave

Swipe to start coding

You are building a simple email filter. Your goal is to allow users to register with any email and mark emails from codefinity.com as allowed.

The function isAllowedEmail takes an email as string.

Use rfind() to find the last '@' symbol in the email.
Compare the result of rfind with -1 to check if the '@' symbol exists. If no '@' is found, return false because the email is invalid.
Initialize a string variable domain as an empty string.
Use a for loop starting from atPos + 1 up to the length of email to iterate over characters after the '@'.
In each iteration, append the character to the domain variable.
If domain equals "codefinity.com", return true.
Otherwise, return false.

Example

isAllowedEmail("alice@example.com") → false
isAllowedEmail("bob@codefinity.com") → true
isAllowedEmail("john.doe@gmail.com") → false
isAllowedEmail("noatdomain.com") → false

Løsning

solution.cpp

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Sektion 3. Kapitel 6

single

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Suggested prompts:

Can you show an example of using the .find() method?

What does string::npos mean in practice?

How is .rfind() different from .find()?

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Method find()

Sometimes, you may need to search for specific text within a string. This can be done using the .find() or .rfind() methods. Let’s begin with the .find() method.

find.h


              1
            
str.find("text to find")

It returns the index of the first character of the first match.

main.cpp


              1234567
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.find("code") << std::endl; // (code)codefinity
}

Here is an example of finding the first "code" starting from a 3-rd character.

main.cpp


              1234567
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.find("code", 3) << std::endl; // __de(code)finity
}

Method rfind()

You can also locate the last occurrence of some text using the .rfind() method.

rfind.h


              1
            
str.rfind("text to find")

While .find() retrieves the first occurrence of text, .rfind() finds the last occurrence and stands for reverse find.

main.cpp


              12345678
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.find("code") << std::endl;
    std::cout << str.rfind("code") << std::endl;
}

Note

If no match is found, both .find() and .rfind() return a special value, string::npos. This value represents no position and indicates that the search was unsuccessful.

main.cpp


              12345678
            
#include <iostream>

int main()
{
    std::string str = "codecodefinity";
    std::cout << str.rfind("abc") << std::endl;
    std::cout << std::string::npos << std::endl;
}

Opgave

Swipe to start coding

You are building a simple email filter. Your goal is to allow users to register with any email and mark emails from codefinity.com as allowed.

The function isAllowedEmail takes an email as string.

Use rfind() to find the last '@' symbol in the email.
Compare the result of rfind with -1 to check if the '@' symbol exists. If no '@' is found, return false because the email is invalid.
Initialize a string variable domain as an empty string.
Use a for loop starting from atPos + 1 up to the length of email to iterate over characters after the '@'.
In each iteration, append the character to the domain variable.
If domain equals "codefinity.com", return true.
Otherwise, return false.

Example

isAllowedEmail("alice@example.com") → false
isAllowedEmail("bob@codefinity.com") → true
isAllowedEmail("john.doe@gmail.com") → false
isAllowedEmail("noatdomain.com") → false

Løsning

solution.cpp

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Var alt klart?

Tak for dine kommentarer!

Sektion 3. Kapitel 6

single