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String comparison

Learn string comparison operators.

String comparison operators

You test whether two strings are equal with ==, and their order with <, >, <=, >=. Comparison is done in dictionary order.

string a = "apple";
string b = "banana";
if (a == b) { /* equal */ }
if (a < b) { /* a comes first */ }

The operators are case-sensitive: "Apple" and "apple" are not equal. Equality checks the string contents character by character; if lengths differ the result is immediately false.

The compare method

The .compare() method of the string class gives more detail. It returns 0 if equal, a negative value if the calling string is smaller, and a positive value if larger.

string a = "apple";
string b = "apple";
int c = a.compare(b);  // c = 0

This method is handy when sorting algorithms need a comparator. For simple equality == is more readable; but when a three-way comparison is needed, .compare() is preferred.

Practice Compare two strings and print

Define string a = "cherry"; and string b = "cherry";. Test equality with if (a == b); if equal, print cout << "same" << endl;. Otherwise print cout << "different" << endl;.

Starter code

main.cpp
#include <iostream>
#include <string>
using namespace std;

int main() {
    string a = "cherry";
    string b = "cherry";
    // compare with ==, print "same" if equal, otherwise "different"
    return 0;
}

Sample solution

main.cpp
#include <iostream>
#include <string>
using namespace std;

int main() {
    string a = "cherry";
    string b = "cherry";
    if (a == b) {
        cout << "same" << endl;
    } else {
        cout << "different" << endl;
    }
    return 0;
}

Expected output

same

Questions and answers

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

1 What does the string class's compare() return for two equal strings?

  • 1
  • -1
  • true
  • 0 Correct answer

Explanation: For equal strings, compare() returns 0.

2 Match each expression with its result

Term Meaning
"a" == "a" equal
"a" < "b" comes first
"b" < "a" comes after

3 Fill in the blank: equality check

Question 
string a = "apple";
string b = "banana";
if (a ____ b) {
    cout << "same";
}
Answer 
string a = "apple";
string b = "banana";
if (a == b) {
    cout << "same";
}

Explanation: == tests whether the contents of two strings are equal.

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