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String and character functions in C++

This post will teach you about the built-in C++ functions that can be used to perform tasks on characters and strings. So, without further ado, let's begin with the "C++ string functions" and then move on to the character functions.

C++ string functions

C++ treats a string as a null-terminated array of characters. In a standard implementation, the string functions require the header file string to provide their prototypes.

Many built-in functions were created by C++ developers to perform tasks related to the strings in the program. However, I will only list and describe the most commonly used ones, or those that are widely used and well-known. So here is a list of the most fundamental and well-known C++ string built-in functions:

length()
compare()
swap()
append()
find()
push_back()
pop_back()
resize()
replace()

Following this paragraph are examples of all of the above C++ string functions, one by one.

C++ length()

The length() function determines the length of the given string. As an example:

C++ Code

#include<iostream>
using namespace std;
int main()
{
   string myString = "codescracker";
   cout<<"Length = "<<myString.length();

   cout<<endl;
   return 0;
}

Output

Length = 12

C++ compare()

The compare() function compares the two strings. If both strings are equal, it returns 0. As an example:

C++ Code

#include<iostream>
using namespace std;
int main()
{
   string myStringOne = "codescracker";
   string myStringTwo = "codescracker";

   int x = myStringOne.compare(myStringTwo);
   if(x==0)
      cout<<"Equal.";
   else
      cout<<"Not equal.";

   cout<<endl;
   return 0;
}

Output

Equal.

C++ swap()

The swap() function swaps the strings. For example:

C++ Code

#include<iostream>
using namespace std;
int main()
{
   string str1 = "codes";
   string str2 = "cracker";
   
   cout<<"Before swap:\n";
   cout<<"str1 = "<<str1<<"\tstr2 = "<<str2;

   str1.swap(str2);
   
   cout<<"\n\nAfter swap:\n";
   cout<<"str1 = "<<str1<<"\tstr2 = "<<str2;

   cout<<endl;
   return 0;
}

Output

Before swap:
str1 = codes    str2 = cracker

After swap:
str1 = cracker  str2 = codes

C++ append()

The append() function adds new text to the string. For example:

C++ Code

#include<iostream>
using namespace std;
int main()
{
   string str1 = "codes";
   string str2 = "cracker";

   cout<<"Before append:\n";
   cout<<"str1 = "<<str1;

   str1.append(str2);

   cout<<"\n\nAfter append:\n";
   cout<<"str1 = "<<str1;

   cout<<endl;
   return 0;
}

Output

Before append:
str1 = codes

After append:
str1 = codescracker

C++ find()

The find() function finds the index number of the specified word (substring) in a string. It returns the index number of the first character of the substring. As an example:

C++ Code

#include<iostream>
using namespace std;
int main()
{
   string str = "I had a lot of fun while learning C++.";
   string word = "fun";

   cout<<"Position = "<<str.find(word);

   cout<<endl;
   return 0;
}

Output

Position = 15

C++ push_back()

The push_back() function adds a new character to the string's end. For example:

C++ Code

#include<iostream>
using namespace std;
int main()
{
   string str = "codescracke";

   cout<<"Before push_back():\n";
   cout<<"str = "<<str;

   str.push_back('r');
   
   cout<<"\n\nAfter push_back('r'):\n";
   cout<<"str = "<<str;

   cout<<endl;
   return 0;
}

Output

Before push_back():
str = codescracke

After push_back('r'):
str = codescracker

C++ pop_back()

The pop_back() function removes the last character from the string. For example:

C++ Code

#include<iostream>
using namespace std;
int main()
{
   string str = "codescracker";

   cout<<"Before pop_back():\n";
   cout<<"str = "<<str;

   str.pop_back();
   
   cout<<"\n\nAfter pop_back():\n";
   cout<<"str = "<<str;

   cout<<endl;
   return 0;
}

Output

Before pop_back():
str = codescracker

After pop_back():
str = codescracke

C++ resize()

The resize() function resizes the string's length. As an example:

C++ Code

#include<iostream>
using namespace std;
int main()
{
   string str = "codescracker.com";

   cout<<"Before resize(5):\n";
   cout<<"str = "<<str;

   str.resize(5);

   cout<<"\n\nAfter resize(5):\n";
   cout<<"str = "<<str;
   cout<<endl;

   return 0;
}

Output

Before resize(5):
str = codescracker.com

After resize(5):
str = codes

C++ replace()

When we need to replace a substring from a string, we use the replace() method. As an illustration:

C++ Code

#include<iostream>
using namespace std;
int main()
{
   string x = "I'm fine. So, how about you?";
   string  y = "not feeling well";

   cout<<"Before replace():\n";
   cout<<"x = "<<x;

   x.replace(4, 4, y);

   cout<<"\n\nAfter replace():\n";
   cout<<"x = "<<x;
   cout<<endl;

   return 0;
}

Output

Before replace():
x = I'm fine. So, how about you?

After replace():
x = I'm not feeling well. So, how about you?

In the preceding example, the first parameter, "4", refers to the position (index); the second parameter, "4", refers to the length or number of characters to be replaced by another string; and the third parameter, "y" (with a value of "not feeling well"), refers to the substring that will replace the content defined by the position and length using the first and second parameters.

C++ character functions

The following list summarizes some important and well-known characters functions available in the C++ programming language:

isalpha() returns nonzero if the argument is an alphabet. The "isalpha" stands for "is alphabet."
islower() returns nonzero if the argument is a lowercase letter.
isupper() returns nonzero if the argument is an uppercase letter.
tolower() returns the lowercase equivalent of the specified argument.
toupper() returns the uppercase equivalent of the specified argument.

For example:

C++ Code

#include<iostream>
using namespace std;
int main()
{
   cout<<islower('A');
   cout<<endl;
   cout<<isupper('A');
   cout<<endl;

   return 0;
}

Output

0
1

The function "tolower('A')" returns the ASCII value of the lowercase 'a'. Similarly, "toupper('a')" returns the ASCII value of uppercase "A."

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