Comparing two strings in C++
Last Updated : 23 Jun, 2022
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 the following two methods
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; } OutputGeeks is not equal to forGeeks forGeeks is greater than Geeks Geeks is equal to Geeks
Time Complexity: O(min(n,m)) where n and m are the length of the strings.
Auxiliary Space: O(max(n,m)) where n and m are the length of the strings.
This is because when string is passed in the function it creates a copy of itself in stack.
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; } OutputGeeks is not equal to forGeeks forGeeks is greater than Geeks Geeks is equal to Geeks
Time Complexity: O(min(n,m)) where n and m are the length of the strings.
Auxiliary Space: O(max(n,m)) where n and m are the length of the strings.
This is because when string is passed in the function it creates a copy of itself in stack.
Differences between C++ Relational operators and compare() :-
- compare() returns an int, while relational operators return boolean value i.e. either true or false.
- 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.
- 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:-
// 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"; The 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 the same manner.