String handling basics in C++ - Mini Project: Build & Apply

String handling basics

📖 Scenario: You are creating a simple program to manage a list of fruit names. You will practice basic string handling in C++.

🎯 Goal: Build a program that stores fruit names, checks for a specific fruit, counts how many fruits have names longer than a certain length, and then prints the results.

📋 What You'll Learn

Create a vector of strings with exact fruit names

Create an integer variable for length threshold

Use a for loop to count fruits with names longer than the threshold

Print the count and whether a specific fruit is in the list

💡 Why This Matters

🌍 Real World

Managing lists of names or items is common in apps like shopping lists, contact managers, or inventory systems.

💼 Career

Basic string handling and loops are foundational skills for software developers working with user input, data processing, and text analysis.

1

Create the fruit list

Create a std::vector<std::string> called fruits with these exact entries: "apple", "banana", "cherry", "date", "elderberry".

C++

#include 
#include 
#include 

int main() {
    // Create the vector fruits with the given fruit names
    // Your code here
    return 0;
}

Hint

Use std::vector<std::string> fruits = { ... }; to create the list.

2

Set the length threshold

Create an int variable called length_threshold and set it to 5.

C++

#include 
#include 
#include 

int main() {
    std::vector fruits = {"apple", "banana", "cherry", "date", "elderberry"};
    // Create the int variable length_threshold and set it to 5
    // Your code here
    return 0;
}

Hint

Write int length_threshold = 5; to create the variable.

3

Count fruits longer than threshold

Create an int variable called count_long and set it to 0. Then use a for loop with variable fruit to iterate over fruits. Inside the loop, increase count_long by 1 if fruit.length() is greater than length_threshold.

C++

#include 
#include 
#include 

int main() {
    std::vector fruits = {"apple", "banana", "cherry", "date", "elderberry"};
    int length_threshold = 5;
    // Create count_long and set to 0
    // Use a for loop with fruit to count fruits longer than length_threshold
    // Your code here
    return 0;
}

Hint

Use for (const std::string& fruit : fruits) to loop over the fruits.

4

Print the results

Use std::cout to print the text "Number of fruits longer than 5: " followed by count_long. Then check if "banana" is in fruits using a for loop with variable fruit. If found, print "Banana is in the list.", otherwise print "Banana is not in the list.".

C++

#include 
#include 
#include 

int main() {
    std::vector fruits = {"apple", "banana", "cherry", "date", "elderberry"};
    int length_threshold = 5;
    int count_long = 0;
    for (const std::string& fruit : fruits) {
        if (fruit.length() > length_threshold) {
            count_long++;
        }
    }
    // Print the count_long with message
    // Check if "banana" is in fruits and print the result
    // Your code here
    return 0;
}

Hint

Use std::cout to print messages and a for loop to find "banana".

Practice

1. What does the following C++ code do?
std::string s = "Hello";
int len = s.length();

easy

A. Changes the string s to "length"

B. Stores the length of the string "Hello" in variable len

C. Prints the string length to the screen

D. Deletes the string s

Solution

1. Step 1: Understand the string initialization

   The code creates a string variable s with the value "Hello".

2. Step 2: Understand the length() function

   The length() function returns the number of characters in the string, which is 5 for "Hello".

3. Final Answer:

   Stores the length of the string "Hello" in variable len -> Option B

4. Quick Check:

   string length = 5 [OK]

Hint: length() returns number of characters in a string [OK]

Common Mistakes:

• Thinking length() changes the string
• Confusing length() with printing
• Assuming length() deletes the string

2. Which of the following is the correct way to declare and initialize a string in C++?

easy

A. std::string s = "Hello";

B. string s = 'Hello';

C. char s = "Hello";

D. string s = Hello;

Solution

1. Step 1: Check string declaration syntax

   In C++, strings are declared using std::string and initialized with double quotes "".

2. Step 2: Analyze each option

   std::string s = "Hello"; uses std::string with double quotes correctly. string s = 'Hello'; uses single quotes which are for single characters. char s = "Hello"; uses char which holds one character, not a string. string s = Hello; misses quotes around Hello.

3. Final Answer:

   std::string s = "Hello"; -> Option A

4. Quick Check:

   Correct string syntax uses std::string and double quotes [OK]

Hint: Use std::string and double quotes for strings [OK]

Common Mistakes:

• Using single quotes for strings
• Using char for multiple characters
• Forgetting quotes around text

3. What is the output of this C++ code?

std::string s = "Hello";
char c = s[1];
std::cout << c << std::endl;

medium

A. o

B. H

C. l

D. e

Solution

1. Step 1: Understand string indexing

   Strings in C++ are zero-indexed, so s[0] = 'H', s[1] = 'e'.

2. Step 2: Identify the character at index 1

   The code stores s[1] in c, which is 'e', then prints it.

3. Final Answer:

   e -> Option D

4. Quick Check:

   Index 1 character = 'e' [OK]

Hint: Remember string indexing starts at 0 [OK]

Common Mistakes:

• Thinking indexing starts at 1
• Confusing characters at different positions
• Expecting the whole string instead of one char

4. Find the error in this code snippet:

std::string s = "Hello";
char c = s.at(5);
std::cout << c << std::endl;

medium

A. No error, prints 'o'

B. Compilation error: cannot assign char

C. Runtime error: out_of_range exception

D. Syntax error: wrong function name

Solution

1. Step 1: Check string length and indexing

   The string "Hello" has length 5, valid indices are 0 to 4.

2. Step 2: Understand s.at(5) behavior

   Accessing s.at(5) is out of range and throws a runtime exception.

3. Final Answer:

   Runtime error: out_of_range exception -> Option C

4. Quick Check:

   Accessing index 5 causes out_of_range error [OK]

Hint: s.at(index) throws error if index invalid [OK]

Common Mistakes:

• Assuming s.at() works like s[] without error
• Ignoring zero-based indexing
• Confusing syntax and runtime errors

5. Given a string std::string s = "apple,banana,cherry";, which code correctly extracts the substring "banana"?

hard

A. std::string sub = s.substr(6, 6);

B. std::string sub = s.substr(5, 6);

C. std::string sub = s.substr(6, 7);

D. std::string sub = s.substr(7, 6);

Solution

1. Step 1: Identify the start index of "banana"

   "apple," has 6 characters (indices 0 to 5), so 'b' starts at index 6.

2. Step 2: Determine length of "banana"

   "banana" has 6 characters.

3. Step 3: Use substr(start, length)

   Calling s.substr(6, 6) extracts 6 characters starting at index 6, which is "banana".

4. Final Answer:

   std::string sub = s.substr(6, 6); -> Option A

5. Quick Check:

   substr(6,6) = "banana" [OK]

Hint: Count start index and length carefully for substr() [OK]

Common Mistakes:

• Off-by-one errors in start index
• Wrong length parameter
• Confusing substr parameters order