The **`compare()` function** is a member function of the standard library in the String class. The function compares strings and returns integers that indicate the difference in the strings. 

# Syntax
```
string1.compare(string2)

//or
string1.compare(pos1, len1, string2)

//or
string1.compare(pos1, len1, string2, pos2, length2)
```
`pos1` is the starting position for `string1` and `len1` dictates the length that would be compared with `string2`. `pos2` and `len2` follow the same conventions.  




# Return value
1) A 0 is returned if the strings are exactly the same.
2) A negative integer is returned if the first string precedes the second one in value OR if the two strings have the same content but the first one is shorter.
3) A positive integer is returned if the first string is greater in value than the second one OR if the two strings have the same content but the first one is longer.

# Code

#include <iostream>
#include <string>

int main ()
{
  std::string str1 ("deep learning");
  std::string str2 ("machine learning");

  std::string s3 ("Educative");
  std::string s4 ("Educative");

  std::string s5 ("hello!");
  std::string s6 ("Hello!");

  std::cout<<str1.compare(str2)<<"\n"; //str1 precedes str2 in sorted order
  std::cout<<s3.compare(s4)<<"\n"; //returns 0
  std::cout<<s5.compare(s6)<<"\n"; //returns 1 cos lower case > uppercase

  if (str1.compare(str2) != 0)
    std::cout << str1 << " is not equal to " << str2 << '\n';

  if (str1.compare(5,8,"learning") == 0)
    std::cout << str1<<" is a type of learning \n";

  if (str1.compare(5,8,str2,8,8) == 0)
    std::cout << "Both the strings contain the phrase 'learning' \n";

  return 0;
}







# Explanation
The following code contains 6 strings, compares them, and generates relevant integers or comments. 

The first compare system prints a negative number because the string `str1` precedes `str2` when sorted, i.e., 'd' of "deep learning" precedes 'm' of "machine learning" in value.

Since the strings `str3` and `str4` are equal, 0 is generated.

The strings `str5` and `str6` generate a positive number (a value greater than 0) since the lowercase `h` in string `str5` has a greater value than the uppercase `H` in string `str6`.

The first `if` statement is executed, since `str1` and `str2` are not equal.

The second `if` statement compares the snippet obtained from index 5 of `str1`, spanning over a length of 8 characters and the string specified as the third argument, i.e., "learning". Since the word "learning" is generated as dictated by the first 2 arguments, the result comes out to be 0 (both strings are equal).

Similarly, the last `if` statement is also executed. The first argument specifies the starting index position from `str1`, the second argument specifies the spanning length, the third argument specifies the second string for comparison, the fourth argument specifies the starting index for `str2`, and the last argument specifies the spanning length of `str2`. Since these two substrings result in "learning", the output comes out to be 0.

What is std::basic_string::compare in C/C++?

Syntax

Return value

Code

Explanation