How to Remove a Character from a String in C++

One of the common tasks in programming is manipulating strings, and one such manipulation is removing a specific character from a string. In this article, we will discuss various ways to remove a character from a string in C++.

Algorithm for Removing a Character from a String in C++

First, let’s see how we can proceed. Here is a step by step algorithm:

1. Include the necessary header files. To use the string class and its functions, we need to include the header file <string>.

2. Declare the string and the character to be removed. Declare a string variable and initialize it with the string from which you want to remove a character. Declare a character variable and initialize it with the character that you want to remove.

3. Find the position of the character to be removed. Use a loop to iterate through the string and find the position of the character to be removed.

4. Remove the character from the string.Once you have found the position of the character to be removed, use one of the following methods to remove it from the string:

• Use the erase() function.
• Use the replace() function.
• Use the substr() function.
• Use the Loop and += operator

5. Print the modified string. After removing the character, print the modified string to see the result.

Four Ways to Remove a Character from a String in C++

There are several approaches to remove a character from a string in C++, and we will discuss a few of them here:

1. Using the erase() function.

The erase() function is a part of the string class in C++, and it can be used to remove a character or a range of characters from a string. To remove a specific character, we can use the erase() function by passing the index of the character to be removed as the argument.

2. Using the replace() function.

The replace() function is another function of the string class in C++, which can be used to replace a character or a range of characters with another character or string. To remove a specific character, we can use the replace() function by replacing the character with an empty string.

3. Using the substr() function.

The substr() function is also a part of the string class in C++, and it can be used to extract a part of the string. To remove a specific character from a string, we can use the substr() function by extracting the part of the string before and after the character to be removed and then concatenating them.

4. Using the loop and += operator

We can use a loop to iterate through the string and create a new string by appending only the characters that are not equal to the character to be removed using the += operator. This method does not use any library functions.

Now let’s get down to writing the code and parsing it.

Using the erase() function

Remove a Character

To remove a single character, we can pass the index of the character to be removed as the first argument and 1 as the second argument to the erase() function.

Here is an example of how to use the erase() function to remove a character from a string in C++:

#include <iostream>
#include <string>

using namespace std;

int main()
{
   // Declare the string and the character to be removed
   string str = "Hello World";
   char ch = 'l';

   // Find the position of the character to be removed
   int pos = 0;
   for (int i = 0; i < str.size(); i++)
   {
      if (str[i] == ch)
      {
         pos = i;
         break;
      }
   }

   // Remove the character from the string
   str.erase(pos, 1);

   // Print the modified string
   cout << "String after removing the character: " << str << endl;

   return 0;
}

Output:

String after removing the character: Heo World

In the above example, we first declare a string str and initialize it with the string “Hello World”. We also declare a character ch and initialize it with the character ‘l’.

Then, we use a loop to iterate through the string and find the position of the character ‘l’ using the if statement. Once the position is found, we store it in the variable pos and exit the loop using the break statement.

Finally, we use the erase() function to remove the character at position pos from the string by passing pos and 1 as arguments. The modified string is then printed using the cout statement.

Remove Multiple Characters

To remove multiple characters from a string using the erase() function, we can pass the starting index and the number of characters to be removed as arguments. For example, to remove the first two characters from the string “Hello World”, we can use the following code:

#include <iostream>
#include <string>

using namespace std;

int main()
{
   // Declare the string
   string str = "Hello World";

   // Remove the first two characters from the string
   str.erase(0, 2);

   // Print the modified string
   cout << "String after removing the characters: " << str << endl;

   return 0;
}

Output:

String after removing the characters: llo World

We again first declare a string str and initialize it with the string “Hello World”. Then, we use the erase() function to remove the first two characters from the string by passing 0 and 2 as arguments. The modified string is then printed using the cout statement.

Note that the erase() function does not return a modified string. It modifies the original string in place. So, if we want to keep the original string unchanged, we need to make a copy of it before using the erase() function.

Remove a Range of Characters from the String

We can also use the erase() function to remove a range of characters from the string. For example, to remove the characters at positions 2 to 5 (inclusive) from the string “Hello World”, we can use the following code:

#include <iostream>
#include <string>

using namespace std;

int main()
{
   // Declare the string
   string str = "Hello World";

   // Remove the characters at positions 2 to 5 from the string
   str.erase(2, 4);

   // Print the modified string
   cout << "String after removing the characters: " << str << endl;

   return 0;
}

Output:

String after removing the characters: He World

In the above example, we use the erase() function to remove the characters at positions 2 to 5 from the string by passing 2 and 4 as arguments. The modified string is then printed using the cout statement.

Using the replace() function

Remove a Character

Here is an example of how to use the replace() function to remove a character from a string in C++:

#include <iostream>
#include <string>

using namespace std;

int main()
{
   // Declare the string and the character to be removed
   string str = "Hello World";
   char ch = 'l';

   // Find the position of the character to be removed
   int pos = 0;
   for (int i = 0; i < str.size(); i++)
   {
      if (str[i] == ch)
      {
         pos = i;
         break;
      }
   }

   // Replace the character with an empty string
   str.replace(pos, 1, "");

   // Print the modified string
   cout << "String after removing the character: " << str << endl;

   return 0;
}

Output:

String after removing the character: Heo World

We declare a string str , initialize it with “Hello World” string. We declare a character ch and initialize it with the character ‘l’.

Then, we use a loop and find the position of  ‘l’ using the if statement. Once the position is found, we store it in the variable pos and exit the loop using the break statement.

Finally, we use the replace() function to replace the character at position pos with an empty string by passing pos, 1, and an empty string as arguments. The modified string is then printed using the cout statement.

Like the erase() function, the replace() function also does not return a modified string. It modifies the original string in place. So, if we want to keep the original string unchanged, we need to make a copy of it before using the replace() function.

Remove a Range of Characters

Let’s use the replace() function to remove a range of characters from the string by replacing them with an empty string.

For example, to remove the characters at positions 2 to 5 (inclusive) from the string “Hello World”, we can use the following code:

#include <iostream>
#include <string>

using namespace std;

int main()
{
   // Declare the string
   string str = "Hello World";

   // Remove the characters at positions 2 to 5 from the string
   str.replace(2, 4, "");

   // Print the modified string
   cout << "String after removing the characters: " << str << endl;

   return 0;
}

Output:

String after removing the characters: He World

Here we use the replace() function to remove the characters at positions 2 to 5 from the string by replacing them with an empty string by passing 2, 4, and an empty string as arguments. The modified string is then printed using the cout statement.

Remove all Occurrences of a Specific Character

If you want to remove all occurrences of a specific character from the string, you can use the replace() function in a loop until all occurrences are removed. Here is an example of how to do this:

#include <iostream>
#include <string>

using namespace std;

int main()
{
   // Declare the string and the character to be removed
   string str = "Hello World";
   char ch = 'l';

   // Remove all occurrences of the character from the string
   while (true)
   {
      size_t pos = str.find(ch);
      if (pos == string::npos)
      {
         break;
      }
      str.replace(pos, 1, "");
   }

   // Print the modified string
   cout << "String after removing the character: " << str << endl;

   return 0;
}

Output:

String after removing the character: Heo Word

We declare str , initialize it and also declare a character ch with the ‘l’.

Then, we use a while loop to iterate until all occurrences of the character ‘l’ are removed from the string. Inside the loop, we use the find() function to find the position of the character ‘l’ in the string. If the character is not found, the loop is exited using the break statement. Otherwise, we use the replace() function to replace the character with an empty string.

Finally, the modified string is printed using the cout statement.

Using the substr() function

Remove a Specific Character

We can use the substr() function to extract the part of the string before and after the character and concatenate them to remove the character.

Let’s look at an example of how to use the substr() function to remove a character in C++:

#include <iostream>
#include <string>

using namespace std;

int main()
{
   // Declare the string and the character to be removed
   string str = "Hello World";
   char ch = 'l';

   // Find the position of the character to be removed
   int pos = 0;
   for (int i = 0; i < str.size(); i++)
   {
      if (str[i] == ch)
      {
         pos = i;
         break;
      }
   }

   // Extract the part of the string before and after the character
   string before = str.substr(0, pos);
   string after = str.substr(pos+1);

   // Concatenate the strings to remove the character
   str = before + after;

   // Print the modified string
   cout << "String after removing the character: " << str << endl;

   return 0;
}

Output:

String after removing the character: Heo World

In the above example, we first declare a string str and initialize it with the string “Hello World”. We also declare a character ch and initialize it with the character ‘l’.

Then, we again use a loop for finding the position of  ‘l’ using the if statement. Once the position is found, we store it in the variable pos and exit the loop using the break statement.

Next, we use the substr() function to extract the part of the string before and after the character ‘l’. We pass 0 and pos as arguments to the substr() function to extract the part of the string before the character, and pos+1 as an argument to extract the part after the character.

Finally, we concatenate the strings before and after using the + operator and store the result in the string str. The modified string is then printed using the cout statement.

Remove all Occurrences of a Specific Character

Here is an example of how to remove all occurrences of a specific character:

#include <iostream>
#include <string>

using namespace std;

int main()
{
   // Declare the string and the character to be removed
   string str = "Hello World";
   char ch = 'l';

   // Remove all occurrences of the character from the string
   while (true)
   {
      size_t pos = str.find(ch);
      if (pos == string::npos)
      {
         break;
      }
      string before = str.substr(0, pos);
      string after = str.substr(pos+1);
      str = before + after;
   }

   // Print the modified string
   cout << "String after removing the character: " << str << endl;

   return 0;
}

Output:

String after removing the character: Heo Word

After all initializations, we use a while loop to iterate until all occurrences of  ‘l’ are removed from the string. Inside the loop, we use the find() function to find the position of ‘l’ in the string. If the character is not found, the loop is exited using the break statement.

Next, we use the substr() function to extract the part of the string before and after the character ‘l’. We pass 0 and pos as arguments to the substr() function to extract the part of the string before the character, and pos+1 as an argument to extract the part after the character.

Finally, we concatenate the strings before and after using the + operator and store the result in the string str. The modified string is then used for the next iteration of the loop.

After all occurrences of the character ‘l’ are removed, the modified string is printed using the cout statement.

Remove a Character Using a Loop and the += operator

To remove a specific character from a string in C++ without using any library function, we can use a loop to iterate through the string and create a new string by appending only the characters that are not equal to the character to be removed.

Let’s look on an example of how to remove a character from a string in C++ without using any library function:

#include <iostream>
#include <string>

using namespace std;

int main()
{
   // Declare the string and the character to be removed
   string str = "Hello World";
   char ch = 'l';

   // Create a new string by appending only the characters that are not equal to the character to be removed
   string new_str = "";
   for (int i = 0; i < str.size(); i++)
   {
      if (str[i] != ch)
      {
         new_str += str[i];
      }
   }

   // Print the modified string
   cout << "String after removing the character: " << new_str << endl;

   return 0;
}

Output:

String after removing the character: Heo World

First we declare and initialize a string str  . Then we declare and initialize a character ch with ‘l’.

Then, we use a loop and create a new string new_str by appending only the characters that are not equal to the character ‘l’ using the if statement and the += operator.

After all, the modified string is printed using the cout statement.

Comparison of all ways to remove characters from a string

Here is a comparison table with the pros and cons of the erase(), replace(), substr() functions, and using a loop and the += operator to remove a character from a string in C++:

Function	Pros	Cons
erase()	Easy to use and understand	Can only remove a contiguous range of characters
replace()	Can replace a contiguous range of characters with another string	Requires an additional string argument
substr()	Can extract a contiguous range of characters	Requires creating two additional strings for the part before and after the character to be removed
Loop and += operator	Can remove any character from the string	Requires a loop and the += operator

In general, the erase() and replace() functions are easier to use and understand, but they can only remove a contiguous range of characters. The substr() function can extract a contiguous range of characters, but it requires creating two additional strings for the part before and after the character to be removed. Using a loop and the += operator allows us to remove any character from the string, but it requires a loop and the += operator.

It is up to you to decide which method is the best to use depending on your specific requirements and preferences.

• If you only want to remove a contiguous range of characters, the erase() or replace() functions may be the best choice.
• If you want to extract a contiguous range of characters, the substr() function may be the best choice.
• If you want to remove any character from the string, using a loop and the += operator may be the best choice.

It is worth noting that the erase() and replace() functions modify the original string, while the substr() function and the loop and += operator create a new string.

• If you want to modify the original string, the erase() or replace() functions may be the best choice.
• If you want to create a new string without modifying the original string, the substr() function or the loop and += operator may be the best choice.

In terms of performance, the erase() and replace() functions may be slightly faster than the substr() function and the loop and += operator, since they do not require creating additional strings or using a loop. However, the difference in performance may not be significant for small strings.

In summary, the best method to remove a character from a string in C++ depends on your specific requirements and preferences. You should consider factors such as ease of use, the ability to remove a contiguous range of characters or any character, and whether you want to modify the original string or create a new string.