Code Optimization Technique (logical AND and logical OR)

Logical AND (&&)

While using && (logical AND), we must put the condition first whose probability of getting false is high so that compiler doesn’t need to check the second condition if the first condition is false.

 #include    // Function to check whether n is odd bool isOdd(int n);    // Function to check whether n is prime bool isPrime(int n);    int main() {     int cnt = 0, n = 10;        // Implementation 1     for (int i = 2; i <= n; i++) {         if (isOdd(i) && isPrime(i))             cnt++;     }        cnt = 0;     n = 10;        // Implementation 2     for (int i = 2; i <= n; i++) {         if (isPrime(i) && isOdd(i))             cnt++;     } }

Consider the above implementation:

In implementation 1, we avoid checking even numbers whether they are prime or not as primality test requires more computation than checking a number for even/odd.
Probability of a number getting odd is more than of it being a prime that’s why we first check whether the number is odd before checking it for prime.

On the other hand in implementation 2, we are checking whether the number is prime or not before checking whether it is odd which makes unnecessary computation as all even numbers other than 2 are not prime but the implementation still checks them for prime.

Logical OR (||)

While using || (logical OR), we must put the condition first whose probability of getting true is high so that compiler doesn’t need to check the second condition if the first condition is true.

 #include    // Function to check whether n is odd bool isEven(int n);    // Function to check whether n is prime bool isPrime(int n);    int main() {     int cnt = 0, n = 10;        // Implementation 1     for (int i = 3; i <= n; i++) {         if (isEven(i) || !isPrime(i))             cnt++;     } }

As described earlier that the probability of a number being even is more than that of it being a non-prime. The current order of execution of the statements doesn’t allow even numbers greater than 2 to be checked whether they are non-prime (as they are all non-primes).

Note: For larger inputs, the order of the execution of statements can affect the overall execution time for the program.

My Personal Notes arrow_drop_up Hello friends, I have a deep knowledge on programming language like C,C++,Java,especially in C and Java I like to do comparative study and likes to ask question ie if , why and why not we In future, i want to be an entrepreneur and really focus on how to improve Education System

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.