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Comparing two string using comparison operators in C++ STL

C++ STL | string comparison: In this article, we are going to see how we can use comparison operators to compare two strings in C++?
Submitted by Radib Kar, on February 27, 2019

String as datatype

In C, we know string basically a character array terminated by \0. Thus to operate with the string we define character array. But in C++, the standard library gives us the facility to use the string as a basic data type like an integer. Like integer comparisons, we can do the same for strings too.

Example

Here is an example with sample input and output:

Like we define and declare,

int i=5, j=7;
Same way, we can do for a string like,

string s1="Include", s2="Help";

Like integers (i==j) , (i>j), (i<j)
We can also do the same like
if(s1==s2)
    cout << 'They are same\n";
else if(s1>s2)
    cout<<s1<<" is greater\n";
else
    cout<<s2<< "s2 is greater\n"; 

Remember, a string variable (literal) need to be defined under "". 'a' is a character whereas "a" is a string.

How comparison between two string works?

'==' operator

Two strings need to be lexicographically same to return true which checking for == operator. "Include" and "Include" is the same. But, "INCLUDE" and "Include" is not same, i.e., case matters.

'>' , '<' operator

This two operator checks which string is greater(smaller) lexicographically. The checking starts from the initial character & checking is done as per ascii value. The checking continues until it faces the same character from both strings. Like,

"Include" > "Help" as 'I' > 'H'
"Include" < "India" as 'c' < 'd'

Header file needed

#include <string>
Or
#include <bits/stdc++.h>

C++ program to compare two strings using comparison operator (==)

#include <bits/stdc++.h>
using namespace std;

void compare(string a, string b) {
  if (a == b)
    cout << "strings are equal\n";
  else if (a < b)
    cout << b << " is lexicografically greater\n";
  else
    cout << a << " is lexicografically greater\n";
}

int main() {
  string s1, s2;

  cout << "enter string1\n";
  cin >> s1;
  cout << "enter string2\n";
  cin >> s2;

  compare(s1, s2);  // user-defined function to comapre

  return 0;
}

Output

First run:
enter string1
Include
enter string2
Help
Include is lexicografically greater

Second run:
enter string1
Include
enter string2
India
India is lexicografically greater