Less Than Operator (<) in C++

The less than operator (<) is a relational operator in C++ used to compare two values. It checks whether the value on the left-hand side is strictly less than the value on the right-hand side.

It evaluates to true if the left operand is less, and false otherwise.

Syntax

operand1 < operand2

• Returns true if operand1 is less than operand2.
• Returns false otherwise.

1. Less Than with Integers

int a = 5, b = 10;
std::cout << (a < b);  // Output: 1 (true)

int a = 15, b = 10;
std::cout << (a < b);  // Output: 0 (false)

2. Less Than with Float and Double

float x = 3.14f;
float y = 6.28f;
std::cout << (x < y);  // Output: 1 (true)

double a = 0.2;
double b = 0.3;
std::cout << (a < b);  // Output: 1 (true)

3. Less Than with Characters

Characters are internally represented using ASCII values, allowing direct numeric comparison.

char a = 'a';  // ASCII 97
char b = 'z';  // ASCII 122
std::cout << (a < b);  // Output: 1 (true)

4. Less Than with Boolean Values

In C++, false is 0 and true is 1. So false < true will return true.

bool a = false;
bool b = true;
std::cout << (a < b);  // Output: 1 (true)

5. Less Than with Strings (std::string)

The std::string class supports lexicographical comparison using the < operator.

#include <string>
std::string a = "apple";
std::string b = "banana";
std::cout << (a < b);  // Output: 1 (true)

std::string a = "zebra";
std::string b = "apple";
std::cout << (a < b);  // Output: 0 (false)

6. Less Than with C-style Strings

Use strcmp() for comparing C-style strings.

#include <cstring>
char a[] = "apple";
char b[] = "banana";
std::cout << (strcmp(a, b) < 0);  // Output: 1 (true)

7. Less Than in Conditions

int marks = 35;
if (marks < 40) {
    std::cout << "Needs improvement.";
}

8. Less Than in Loops

int i = 0;
while (i < 5) {
    std::cout << i << " ";
    i++;
}

Output: 0 1 2 3 4

9. Mixed Data Type Comparison

int a = 10;
float b = 10.5f;
std::cout << (a < b);  // Output: 1 (true)

10. Practice Problems

Problem 1: Simple Voting Age Check

int age = 15;
if (age < 18) {
    std::cout << "Too young to vote.";
}

Problem 2: Compare Two Characters

char a = 'b';
char b = 'f';
if (a < b) {
    std::cout << "a comes before b";
}

Problem 3: String Sorting Comparison

std::string name1 = "Anna";
std::string name2 = "Bella";
if (name1 < name2) {
    std::cout << name1 << " comes before " << name2;
}

Summary Table

Best Practices

• Use < when you want to check if a value is smaller than another.
• Avoid direct comparison of raw C-style strings using <; use strcmp() instead.
• Be mindful of floating-point precision in comparisons.
• Character and string comparisons follow ASCII/lexicographical order.