The or Operator in C++

1. the Logical OR Operator in C++
2. the Bitwise OR Operator in C++
3. Conclusion

This article explains OR operators in C++ and their use cases. Like any other programming language, C++ has logical OR and bitwise OR; let’s look at them one by one.

the Logical OR Operator in C++

We use a logical operator to compare two or more operands/expressions and return true or false values. These are useful in decision-making scenarios.

Logical OR is represented using ||.

Syntax:

expression1 || expression2

The logical OR operator || returns:

1. true - if at least one operand or expression is true.
2. false - if and only if all the operands are false.

The truth table of logical OR ||.

A and B are operands.

We can see only when both the operands are false; we get the output as false. In C or C++, false is zero and true is any non-zero value; generally, it is represented using integer 1.

Example:

Let’s see how logical OR is used in decision-making. Consider a situation where a user inputs a lowercase character and wants to know whether it’s a vowel or a consonant.

#include <iostream>
using namespace std;

int main() {
  char ch;
  cin >> ch;

  if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') {
    cout << "It's is a VOWEL.";
  } else
    cout << "It's a consonant";
}

If the input is z, all the OR conditions inside the if statement are false, it is evaluated as false, and the if condition fails. Then the else block is executed.

Output:

z
It's a consonant

One interesting property to remember about the logical OR is that if the left-hand side part is true, the right-hand side part is not evaluated because the whole expression is true now anyway.

Meaning in expression1||expression2 if expression1 is true, expression2 is not evaluated.

Example code:

#include <iostream>
using namespace std;

int main() {
  int a = 10;
  int b = (a = a > 5 ? 25 : 0) || 0;

  cout << "Value of a " << a << endl;
  cout << "Value of b " << b << endl;

  // part two
  int x = 9;
  int c = (x = 0) || (x = 6789);

  cout << "Value of x " << x << endl;
  cout << "Value of c " << c << endl;
}

Output:

Value of a 25
Value of b 1
Value of x 6789
Value of c 1

Explanation: (a=a>5?25:0) is evaluated as true because a is greater than 5 and 25 is assigned to a, and in C++ other than 0(false), all values are considered as true.

Since the left-hand side part of logical OR is true right-hand side is not evaluated; the overall expression value is true that is 1 and is assigned to b.

Now part two of the program c = (x=0) || (x=6789), LHS x=0 means it’s false, so RHS is evaluated x=6789 since any value other than zero is true, the whole expression becomes true now, and 1 is assigned to c.

the Bitwise OR Operator in C++

A single vertical line | represents the bitwise OR. The main difference between logical and bitwise operators is that the result of logical operators (&&, ||, and !) is either 0(false) or 1(true), but the result of a bitwise operator is an integer value.

The | (bitwise OR) in C or C++ takes two numbers as operands and does OR on every bit of two numbers and returns the result.

Example code:

#include <iostream>
using namespace std;

int main() {
  int a = 2;
  int b = 4;

  int c = a || b;  // logical OR

  int d = a | b;  // bitwise OR

  cout << "Value of c " << c << endl;
  cout << "value of d " << d << endl;
}

Output:

Value of c 1
value of d 6

Explanation: For a||b, a=2, which is a non-zero value, is evaluated as true, so the value of c becomes true.

For a|b, we have to first convert a and b in binary format and then apply OR on each bit, a = 010 and b = 100 in binary, and if we apply OR on each bit, we get output as 6, which is assigned to the variable d.

 0 1 0   this is a=2
 1 0 0    this is b=4
-------
 1 1 0  //this is 6 in decimal
-------

Conclusion

We learned about logical and bitwise OR operators in this article.

We understood that logical OR is used for decision making, and any non-zero operands/expressions are considered 1(true), whereas in bitwise OR, the operation is applied to each bit, and an integer value is returned as output.