added: compare() method for strings in c++

content/cpp/concepts/strings/terms/compare/compare.md

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+---
+Title: '.compare()'
+Description: 'Compares two strings lexicographically and returns an integer indicating their relative order.'
+Subjects:
+  - 'Computer Science'
+  - 'Game Development'
+Tags:
+  - 'Comparison'
+  - 'Functions'
+  - 'Methods'
+  - 'Strings'
+CatalogContent:
+  - 'learn-c-plus-plus'
+  - 'paths/computer-science'
+---
+
+In C++, the **`.compare()`** method compares two strings lexicographically (dictionary order) and returns an integer that indicates their relative order. The comparison is done character by character based on ASCII values.
+
+## Syntax
+
+```pseudo
+string1.compare(string2);                              // Compares string1 with string2.
+string1.compare(pos, len, string2);                    // Compares a substring of string1 starting at pos with length len to the entirety of string2.
+string1.compare(pos, len, string2, subpos, sublen);    // Compares a substring of string1 (starting at pos, length len) with a substring of string2 (starting at subpos, length sublen)
+```
+
+**Parameters:**
+
+- `string1`: The string object calling the `.compare()` method.
+- `string2`: The string to compare with.
+- `pos` (optional: Starting position in `string1` for comparison
+- `len` (optional): The number of characters to compare from `string1` starting at `pos`.
+- `subpos` (optional): The starting position in `string2` from which to begin comparison.
+- `sublen` (optional): The number of characters to compare from `string2` starting at `subpos`.
+
+**Return values:**
+
+- Returns `0` if the strings are equal
+- Returns a negative value (< 0) if `string1` is lexicographically less than `string2`
+- Returns a positive value (> 0) if `string1` is lexicographically greater than `string2`
+
+## Example
+
+This example demonstrates the usage of the `.compare()` method:
+
+```cpp
+#include <iostream>
+#include <string>
+
+int main() {
+  std::string str1 = "apple";
+  std::string str2 = "banana";
+  std::string str3 = "apple";
+
+  int result1 = str1.compare(str2);
+  int result2 = str1.compare(str3);
+  int result3 = str2.compare(str1);
+
+  std::cout << "apple vs banana: " << result1 << std::endl;
+  std::cout << "apple vs apple: " << result2 << std::endl;
+  std::cout << "banana vs apple: " << result3 << std::endl;
+
+  return 0;
+}
+```
+
+The output of this code is:
+
+```shell
+apple vs banana: -1
+apple vs apple: 0
+banana vs apple: 1
+```
+
+## Codebyte Example
+
+Run the following codebyte to understand how the `.compare()` method works:
+
+```codebyte/cpp
+#include <iostream>
+#include <string>
+
+int main() {
+  std::string fruit1 = "apple";
+  std::string fruit2 = "orange";
+
+  int comparison = fruit1.compare(fruit2);
+
+  if (comparison < 0) {
+    std::cout << fruit1 << " comes before " << fruit2 << " alphabetically" << std::endl;
+  } else if (comparison > 0) {
+    std::cout << fruit1 << " comes after " << fruit2 << " alphabetically" << std::endl;
+  } else {
+    std::cout << fruit1 << " and " << fruit2 << " are the same" << std::endl;  }
+
+  return 0;
+}
+```
+
+## Frequently Asked Questions
+
+### 1. What is the difference between `.compare()` and `==` operator?
+
+The `==` operator returns a boolean (`true` or `false`) indicating whether two strings are equal. The `.compare()` method returns an integer indicating the _relative order_ of the strings: less than, equal to, or greater than.
+
+### 2. Can `.compare()` be used for case-insensitive comparison?
+
+No, `.compare()` is case-sensitive by default. To perform a case-insensitive comparison, try converting both strings to the same case using methods like `std::transform()` with `::tolower`, or use a custom comparator.
+
+### 3. What happens when comparing strings of different lengths?
+
+If one string is a prefix of the other, the shorter string is considered lexicographically smaller:
+
+```cpp
+std::string a = "app";
+std::string b = "apple";
+bool result = a.compare(b) < 0; // true
+```