C++ Strings: std::string, Operations & String Algorithms

Module 7: Strings in C++

A string is a sequence of characters used to store and manipulate text. C++ supports two types of strings:

• C-Style Strings (Character Arrays)
• std::string (Standard Library String)

The std::string class is recommended because it is easier, safer, and provides many built-in functions.

1. C-Style Strings

A C-style string is an array of characters terminated with the null character (\0).

Example

cppCopy
1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    char name[] = "Ankit";
8
9    cout << name;
10
11    return 0;
12}

Output

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1Ankit

2. std::string

The std::string class provides powerful functions for working with text.

Example

cppCopy
1#include <iostream>
2#include <string>
3
4using namespace std;
5
6int main()
7{
8    string name = "Ankit";
9
10    cout << name;
11
12    return 0;
13}

Output

textCopy
1Ankit

String Operations

length()

Returns the number of characters in a string.

Example

cppCopy
1#include <iostream>
2#include <string>
3
4using namespace std;
5
6int main()
7{
8    string text = "Tech3Space";
9
10    cout << text.length();
11
12    return 0;
13}

Output

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110

substr()

Returns a portion of a string.

Example

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1string text = "Programming";
2
3cout << text.substr(0, 7);

Output

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1Program

find()

Searches for the first occurrence of a substring.

Example

cppCopy
1string text = "Welcome to C++";
2
3cout << text.find("C++");

Output

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111

erase()

Removes characters from a string.

Example

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1string text = "Hello World";
2
3text.erase(5, 6);
4
5cout << text;

Output

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1Hello

replace()

Replaces part of a string.

Example

cppCopy
1string text = "Hello Java";
2
3text.replace(6, 4, "C++");
4
5cout << text;

Output

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1Hello C++

append()

Adds text to the end of a string.

Example

cppCopy
1string first = "Tech3";
2first.append("Space");
3
4cout << first;

Output

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1Tech3Space

String Algorithms

Palindrome

A palindrome reads the same forwards and backwards.

Example

cppCopy
1#include <iostream>
2#include <string>
3#include <algorithm>
4
5using namespace std;
6
7int main()
8{
9    string text = "madam";
10    string rev = text;
11
12    reverse(rev.begin(), rev.end());
13
14    if (text == rev)
15        cout << "Palindrome";
16    else
17        cout << "Not Palindrome";
18
19    return 0;
20}

Output

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1Palindrome

Reverse String

Example

cppCopy
1#include <iostream>
2#include <algorithm>
3
4using namespace std;
5
6int main()
7{
8    string text = "Hello";
9
10    reverse(text.begin(), text.end());
11
12    cout << text;
13
14    return 0;
15}

Output

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1olleH

Character Frequency

Count the occurrence of each character.

Example

cppCopy
1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    string text = "banana";
8    int count = 0;
9
10    for (char ch : text)
11    {
12        if (ch == 'a')
13            count++;
14    }
15
16    cout << count;
17
18    return 0;
19}

Output

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13

String Compression

String compression replaces consecutive repeated characters with the character followed by its count.

Example:

textCopy
1aaabbcccc

Compressed Output

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1a3b2c4

Example

cppCopy
1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    string str = "aaabbcccc";
8
9    for (int i = 0; i < str.length();)
10    {
11        char current = str[i];
12        int count = 0;
13
14        while (i < str.length() && str[i] == current)
15        {
16            count++;
17            i++;
18        }
19
20        cout << current << count;
21    }
22
23    return 0;
24}

Output

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1a3b2c4

Comparison of String Functions

Best Practices

• Prefer std::string over C-style strings.
• Use built-in string functions whenever possible.
• Validate indices before using substr() or erase().
• Use getline() to read strings containing spaces.
• Use algorithms like reverse() from the Standard Library for cleaner code.

Practice Problems

1. Find the length of a string.
2. Reverse a string.
3. Check whether a string is a palindrome.
4. Count vowels and consonants.
5. Count the frequency of each character.
6. Remove duplicate characters.
7. Replace one word with another.
8. Compress a string.
9. Find the first occurrence of a substring.
10. Concatenate two strings.

Interview Questions

1. What is the difference between C-style strings and std::string?
2. What does the length() function return?
3. How does substr() work?
4. What is the purpose of find()?
5. How do erase() and replace() differ?
6. What is string compression?
7. How can you check if a string is a palindrome?
8. How do you reverse a string in C++?

Summary

In this module, you learned:

• The difference between C-style strings and std::string.
• How to use common string operations like length(), substr(), find(), erase(), replace(), and append().
• How to solve common string problems such as palindrome checking, reversing a string, counting character frequency, and string compression.
• Best practices and practical exercises for mastering string manipulation in C++.

Next Module: Module 8: Pointers — Pointer Basics, Pointer Arithmetic, Pointers and Arrays, Dynamic Memory Allocation (new and delete), Null Pointers, Void Pointers, Function Pointers, Smart Pointers, and Memory Management.