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Different Ways to Compare Strings in C++
2022-06-12 18:00:12

Different Ways to Compare Strings in C++

This section will go over the many methods for comparing strings in the C++ programming language. The string comparison checks if the first string is equal to another string. HELLO and Hello are two distinct strings.

In the C++ programming language, there are several techniques to compare strings, as follows:

  • strcmp ( ) is a function that can be used to compare two strings.
  • Using the method compare ( )
  • Relational Operators in Use
  • Using the for loop and the If condition
  • Using a custom function

strcmp ( ) function

The strcmp ( ) method is a string.h header file pre-defined library function. The strcmp () method lexicographically compares two strings. This indicates that the strcmp ( ) method compares the first and second strings character by character until both strings are identical or a NULL character is found.

Following is the syntax:

int strcmp ( const char *leftstr, const char *rightstr );   
  • The letters of the right string are defined by leftstr.
  • The characters of the right-wing unit are defined by rightstr.

Let's use the strcmp() function in C++ to build a programme that compares strings:

#include < iostream >  
#include < bits/stdc++.h >
#include < stdlib >
using namespace std ;  
#include < string.h >  
int main ( )  
{  
    // declare strings  
    const char * str1 = " This is Tutorial And Example" ;  
    const char * str2 = " This is Tutorial And Example " ;  
    const char * str3 = " Tutorial And Example " ;  
    const char * str4 = " Tutorial And Example " ;  
    cout << " String 1: " << str1 << endl ;  
    cout << " String 2: " << str2 << endl ;  
    // use strcmp ( ) function to validate the strings are equal  
    if ( strcmp ( str1 , str2 ) == 0 )  
    {  
        cout << " \n Both strings are equal. " << endl ;  
    }  
    else   
        {      
        cout << " The strings are not equal. " << endl ;  
    }  
    cout << " \n String 3: " << str3 << endl ;  
    cout << " String 4: " << str4 << endl ;  
    // use strcmp ( ) function to validate the strings are equal  
    if ( strcmp ( str3 , str4 ) == 0 )  
    {  
        cout << " \n Both strings are equal. " << endl ;  
    }     
    else   
        cout << " \n The strings are not equal. " ;      
return 0 ;  
}  

OUTPUT:

String 1: This is Tutorial And Example
String 2:  This is Tutorial And Example
Both strings are equal. 
String 3:  Tutorial And Example
String 4:  Tutorial And Example
The strings are not equal.

Explanation:

From the left side to the end of both strings, the leftstr string compares each character with the second string. The strcmp () method returns equal strings when the strings are equal. Otherwise, the wires will not fit.

compare ( ) function

The C++ language's compare ( ) function is a pre-defined library function. Based on the matching cases, the compare ( ) method compares two strings.

Following is the syntax:

int compare ( const string &str ) const ;   

Let's make simple software that uses the C++ compare ( ) function to compare two strings:

#include < iostream >  
#include < bits/stdc++.h >
#include < stdlib >
using namespace std ;  
int main ( )  
{  
    string str1 , str2 ; // declare string variable  
    cout << " enter the string 1: " ;   
    cin >> str1 ;   
    cout << " enter the string 2: " ;  
    cin >> str2 ;   
    // use compare ( ) function to compare the second string with first string  
    int i = str1 . compare ( str2 ) ;  
    if ( i < 0 )  
    {  
        cout << str1 << " is smaller than " << str2 << " string" << endl ;  
    }  
    else if ( i > 0 )  
    {  
        cout << str2 << " is greater than " << str1 << " string." << endl ;  
    }  
    else // i == 0 ;  
    {  
        cout << " Both strings are equal." ;  
    }  
return 0 ;  
}

OUTPUT:

1st Run:
Enter the string 1: Tutorial And Example
Enter the string 2: Tutorial And Example
Program is smaller than program string
2nd Run:
Enter the string 1: JAVATPOINT
Enter the string 2: JAVATPOINT
Both strings are equal.  

Explanation:

  • The method returns 0 if two strings are the same
  • If the first string's character value is less than the second string's, the method returns 0.
  • The method returns more than 0 or >0 if the second string is longer than the first.

Relation Operator

In C++, it's the operator for comparing two textual or numerical values. Relational operators in C++ include the ' == ', ' != ',  >, and operators. However, to compare the text quickly, we just require two operators: ' == ' equal to and ' != ' not equal to a relational operator.

Following is the syntax:

String1 == string2  // In this case, we'll use the double equal to operator.
Or   
String1 != string2 // We utilize the not equal to operator in this case.

NOTE:

In C++, the Equal to (==) operator is used to compare two strings.

Let's make a C++ program that compares strings with the equal to (==) operator./co

#include < iostream >  
#include < bits/stdc++.h >
#include < stdlib >
using namespace std ;  
int main ( )  
{  
    // declare string variables  
    string str1 ;  
    string str2 ;  
    cout << " enter the String 1: " << endl ;   
    cin >> str1 ;  
    cout << " enter the String 2: " << endl ;  
    cin >> str2 ;  
      
    // use ' == ' equal to operator to check the equality of the string  
    if ( str1 == str2 )  
    {  
        cout << " String is equal." << endl ;  
    }  
    else  
    {  
        cout << " String is not equal." << endl ;  
    }  
    return 0 ;  
}  

OUTPUT:

Enter the String 1:
Tutorial And Example
 Enter the String 2:
Tutorial And Example
String is not equal.
2nd Execution: 
Enter the String 1:
This is Tutorial And Example
Enter the String 2:
This is Tutorial And Example
String is equal.

Explanation:

In the above program in C++ we shown the use of == operator. We are checking if the str1 and str2 is equal and if they are equal then print that string are equal.

NOTE:

The Not Equal To ( != ) Relational Operator is used to compare two strings.

Let's use the Not Equal To ( != ) operator in C++ to develop a program that compares whether the strings are equal or not.

#include < iostream >  
#include < bits/stdc++.h >
#include < stdlib >
using namespace std ;  
int main ( )  
{  
    // declare string variables  
    string str1 ;  
    string str2 ;  
    cout << " enter the String 1: " << endl ;  
    cin >> str1 ;  
    cout << " enter the String 2: " << endl ;  
    cin >> str2 ;  
    // use ' != ' not equal to operator to check the equality of the string  
    if ( str1 != str2 )  
    {  
        cout << " String is not equal." << endl ;  
    }  
    else  
    {  
        cout << " String is equal." << endl ;  
    }  
    return 0 ;  
}  

OUTPUT:

Enter the String 1:
This is Tutorial And Example
 Enter the String 2:
This is Tutorial And Example
 String is not equal.
2nd Run: 
Enter the String 1:
Hey
 Enter the String 2:
Hey
 String is equal.

Explanation:

In the above example of a program in C++, we have shown the use of != operator. We are checking if str1 is not equal to str2 and if this statement is true then doing the printing part.

In C++, use for loop and if statement to compare two strings:

Let's use for loop and if statement in C++ to develop a program that compares whether the strings are equal or not:

#include < iostream >  
using namespace std ;  
int main ( )  
{  
    char s1 [ 50 ] , s2 [ 50 ] ; // declare character array  
    int i, disp;  
    cout << " enter the String 1: " << endl;  
    cin >> s1;  
    cout << " enter the String 2: " << endl;  
    cin >> s2;  
    for (i = 0; s1[i] == s2[i] && s1[i] == '\0'; i++);  
    if (s1[i] < s2[i])  
    {  
        cout << " String 1 is less than String 2";  
    }  
    else if (s1[i] > s2[i])  
    {  
        cout << " String 2 is less than String 1";  
    }  
    else  
    {  
        cout << " String 1 is equal to String 2";  
    }  
    return 0;  
 }  

OUTPUT:

Enter the String 1:
MOST WELCOME!
Enter the String 2:
MOST WELCOME!
String 1 is equal to String 2

Explanation:

In the above example of a program in C++,we declare a character string and with the help of for loop we are checking if string 1 is equal to string 2.

In C++, use the User-defined function to compare two strings

Let's utilize the user-defined function in C++ to make a simple program that compares the first string to another string.

#include <iostream>  
using namespace std;  
void RelationalCompare ( string str1, string str2)  
{  
    // use relational not equal operator  
    if ( str1 != str2)  
    {  
        cout << str1 << " is not equal to " << str2 << " string. " << endl;  
        if (str1 > str2)  
        {  
            cout << str1 << " is greater than " << str2 << " string." << endl;  
        }  
        else  
        {  
            cout << str2 << " is greater than " << str1 << " string." << endl;      
        }  
    }  
        else  
            cout << str1 << " is equal to " << str2 << " string." << endl;  
}  
int main ()  
{  
    string str1 ( "Tutorial");  
    string str2 ( "And Example");  
    // call function  
    RelationalCompare (str1, str2);  
    string str3 ("Tutorial And Example");  
    string str4 ("Tutorial And Example");  
    RelationalCompare (str3, str4);  
    return 0;  
}  

OUTPUT:

Tutorial is not equal to And Examples string.
And Example is greater than Tutorial string.
Tutorial And Example is equal Tutorial And Example to string.

Explanation:

In the above example of a program in C++, we have shown the use of user define function to compare two string. We have created a function called RelationalCompare which takes two string as a parameter and perform its function recursively.