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Comparing two strings in C++
  • Difficulty Level : Basic
  • Last Updated : 02 Nov, 2020

Given two strings, how to check if the two strings are equal or not. 
Examples: 

Input  : ABCD, XYZ
Output : ABCD is not equal to XYZ
         XYZ is greater than ABCD

Input  : Geeks, forGeeks
Output : Geeks is not equal to forGeeks
         forGeeks is greater than Geeks

This problem can be solved using any of following two methords  

  • C++ Relational operators

CPP




// CPP code to implement relational
// operators on string objects
#include <iostream>
using namespace std;
 
void relationalOperation(string s1, string s2)
{
 
    if (s1 != s2)
    {
        cout << s1 << " is not equal to " << s2 << endl;
        if (s1 > s2)
            cout << s1 << " is greater than " << s2 << endl;
        else
            cout << s2 << " is greater than " << s1 << endl;
    }
    else
        cout << s1 << " is equal to " << s2 << endl;
}
 
// Driver code
int main()
{
    string s1("Geeks");
    string s2("forGeeks");
    relationalOperation(s1, s2);
    string s3("Geeks");
    string s4("Geeks");
    relationalOperation(s3, s4);
    return 0;
}
Output
Geeks is not equal to forGeeks
forGeeks is greater than Geeks
Geeks is equal to Geeks
  • std:: Compare() 

CPP




// CPP code perform relational
// operation using compare function
#include <iostream>
 
using namespace std;
 
void compareFunction(string s1, string s2)
{
    // comparing both using inbuilt function
    int x = s1.compare(s2);
 
    if (x != 0) {
        cout << s1
             << " is not equal to "
             << s2 << endl;
        if (x > 0)
            cout << s1
                 << " is greater than "
                 << s2 << endl;
        else
            cout << s2
                 << " is greater than "
                 << s1 << endl;
    }
    else
        cout << s1 << " is equal to " << s2 << endl;
}
 
// Driver Code
int main()
{
    string s1("Geeks");
    string s2("forGeeks");
    compareFunction(s1, s2);
    string s3("Geeks");
    string s4("Geeks");
    compareFunction(s3, s4);
    return 0;
}
Output
Geeks is not equal to forGeeks
forGeeks is greater than Geeks
Geeks is equal to Geeks

Differences between C++ Relational operators and compare() :-  



  1. compare() returns int, while relational operators return boolean value i.e. either true or false. 
  2. A single Relational operator is unique to a certain operation, while compare() can perform lots of different operations alone, based on the type of arguments passed.
  3. We can compare any substring at any position in a given string using compare(), which otherwise requires the long procedure of word by word extraction of string for comparison using relational operators. 

Example :- 

  • Using compare() 
// Compare 3 characters from 3rd position
// (or index 2) of str1 with 3 characters 
// from 4th position of str2. 
if (str1.compare(2, 3, str2, 3, 3) == 0)
   cout<<"Equal";
else
   cout<<"Not equal";
  • Using Relational operator 
for (i = 2, j = 3; i <= 5 && j <= 6; i++, j++)    
{ 
    if (s1[i] != s2[j])
       break;
}
if (i == 6 && j == 7)
    cout << "Equal";
else
    cout << "Not equal";

Above example clearly shows how compare() reduces lots of extra processing, therefore it is advisable to use it while performing substring comparison at some position, otherwise both perform almost in same manner.

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