String comparison

Learn string comparison operators.

String comparison operators

You test whether two strings are equal with ==, and their order with <, >, <=, >=. Comparison is done in dictionary order.

string a = "apple";
string b = "banana";
if (a == b) { /* equal */ }
if (a < b) { /* a comes first */ }

The operators are case-sensitive: "Apple" and "apple" are not equal. Equality checks the string contents character by character; if lengths differ the result is immediately false.

The compare method

The .compare() method of the string class gives more detail. It returns 0 if equal, a negative value if the calling string is smaller, and a positive value if larger.

string a = "apple";
string b = "apple";
int c = a.compare(b);  // c = 0

This method is handy when sorting algorithms need a comparator. For simple equality == is more readable; but when a three-way comparison is needed, .compare() is preferred.

Exercise Compare two strings and print

Define string a = "cherry"; and string b = "cherry";. Test equality with if (a == b); if equal, print cout << "same" << endl;. Otherwise print cout << "different" << endl;.

Show example solution

#include <iostream>
#include <string>
using namespace std;

int main() {
    string a = "cherry";
    string b = "cherry";
    if (a == b) {
        cout << "same" << endl;
    } else {
        cout << "different" << endl;
    }
    return 0;
}

Test yourself

What does the string class's compare() return for two equal strings?
- 1
- -1
- true
- 0
Show answer

0 — For equal strings, compare() returns 0.
Match each expression with its result

"a" == "a"

equal
"a" < "b"

comes first
"b" < "a"

comes after

Fill in the blank: equality check

string a = "apple";
string b = "banana";
if (a ____ b) {
    cout << "same";
}

Show answer

string a = "apple";
string b = "banana";
if (a == b) {
    cout << "same";
}

Next lesson: String modification

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