CodeBlanks Logo Icon CodeBlanks
Login Register

String length

Learn the string length with .length() and .size().

length and size

To find how many characters a std::string has you use the length or size method. Both return the same value: std::string w = "Welcome"; std::cout << w.length(); prints 7.

length is preferred when working with text because it reads naturally; size is used for consistency with STL containers. The return type is size_t, an unsigned integer; you should not expect a negative value.

Validating with length

A common use of the length method is validating user input. For example, you can check whether a password has at least 8 characters with if (password.length() >= 8).

Such checks catch wrong or incomplete input early. Because length returns a numeric value, you can use comparison operators (>, <, ==) directly on it.

Practice Print the string length

The word variable is set to "Welcome". Print word.length() with std::cout. The output on a single line must be 7.

Starter code

main.cpp
#include <iostream>
#include <string>

int main() {
    std::string word = "Welcome";
    // Print the length
    return 0;
}

Sample solution

main.cpp
#include <iostream>
#include <string>

int main() {
    std::string word = "Welcome";
    std::cout << word.length() << std::endl;
    return 0;
}

Expected output

7

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Match each method to its job

Term Meaning
.length() Character count
.size() Character count (same)
.substr() Takes a part
.append(x) Appends at the end

2 What does std::string w = "Welcome"; w.length() return?

main.cpp
std::string w = "Welcome";
w.length()
  • 7 Correct answer
  • 5
  • 6
  • 8

Explanation: "Welcome" has 7 characters; length() returns 7.

3 Write the length call

Question 
std::string w = "Welcome";
int n = w____;
Answer 
std::string w = "Welcome";
int n = w.length();

Explanation: .length() returns the character count.

All lessons in Beginner

1 C++ basics

  1. What is C++?
  2. Your first program
  3. std::cout
  4. std::cin
  5. Comments
  6. Summary - C++ basics

2 Variables

  1. Declaring variables
  2. auto
  3. const
  4. constexpr
  5. Type conversion
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. bool and char
  4. std::string
  5. sizeof
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Bitwise operators
  6. Summary - Operators

6 Strings

  1. std::string basics
  2. String concatenation
  3. String length
  4. Substring
  5. String search
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. The switch statement
  4. The ternary operator
  5. Nested conditionals
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range-based for
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding products
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. C-style arrays
  2. Array access
  3. std::array
  4. Multidimensional arrays
  5. Arrays and loops
  6. Summary - Arrays

11 std::vector

  1. Declaring vectors
  2. push_back
  3. size and at
  4. Vector access
  5. Vector loop
  6. Summary - std::vector

12 Functions

  1. Defining functions
  2. Return values
  3. Parameters
  4. Function overloading
  5. Default parameters
  6. Summary - Functions

13 References

  1. What is a reference?
  2. Declaring references
  3. Reference parameters
  4. const references
  5. Dangling references
  6. Summary - References

14 Pointer basics

  1. What is a pointer?
  2. The & address operator
  3. Pointer dereference
  4. nullptr
  5. Pointer arithmetic
  6. Summary - Pointer basics

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. String streams
  2. stoi and stod
  3. to_string
  4. String comparison
  5. String modification
  6. Summary - Advanced strings

17 Structs

  1. Defining structs
  2. Using structs
  3. Struct and function
  4. Array of structs
  5. Nested structs
  6. Summary - Structs

18 Exception basics

  1. try/catch
  2. throw
  3. std::exception
  4. Custom exceptions
  5. catch all
  6. Summary - Exceptions

19 Namespaces

  1. Defining namespaces
  2. using
  3. std namespace
  4. Nested namespaces
  5. Namespace alias
  6. Summary - Namespaces

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together