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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.

h

indexing

copy

              
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.

cpp

main

copy

              
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.

cpp

main

copy

              
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:

h

at

copy

              
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.

cpp

main

copy

              
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:

cpp

main

copy

              
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

Your task is to check if we can add characters to the end of a string that way.

  1. Figure the index of the last character in a string.
  2. Assign 'y' to the index index of last character + 1 of str.

Løsning

cpp

solution

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book
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.

h

indexing

copy

              
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.

cpp

main

copy

              
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.

cpp

main

copy

              
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:

h

at

copy

              
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.

cpp

main

copy

              
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:

cpp

main

copy

              
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

Your task is to check if we can add characters to the end of a string that way.

  1. Figure the index of the last character in a string.
  2. Assign 'y' to the index index of last character + 1 of str.

Løsning

cpp

solution

Switch to desktopSkift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder
Var alt klart?

Hvordan kan vi forbedre det?

Tak for dine kommentarer!

close

Awesome!

Completion rate improved to 4.35

Stryg for at vise menuen

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