#StayAtHome ×  # Sanjib Sinha

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97

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• Rank
Regular Member
• Birthday 07/18/1965

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• Website URL
http://sanjib.me

## Profile Information

• Gender
Male
• Location
Kolkata
• Interests
story telling, web programming
• Age
49
1. Thanks IThinkMyBrainHurtsI guessed something like this. But why should I go for such complexity? Please consider this code to test the primality: function is_prime(\$num) { for(\$i=2; \$i<= (int)sqrt(\$num); \$i++){ if(\$num % \$i == 0) { return false; } } return true; } if(is_prime(119)){ echo 'Prime'; } else { echo 'Not Prime'; } //output not prime
2. I had searched web and found some of them very interesting and few of them seem complex like this one in wiki: function isPrime(\$n) { if (\$n <= 3) { return \$n > 1; } else if (\$n % 2 === 0 || \$n % 3 === 0) { return false; } else { for (\$i = 5; \$i * \$i <= \$n; \$i += 6) { if (\$n % \$i === 0 || \$n % (\$i + 2) === 0) { return false; } } return true; } } Specially this part: for (\$i = 5; \$i * \$i <= \$n; \$i += 6) { if (\$n % \$i === 0 || \$n % (\$i + 2) === 0) { return false; } } It started from 5. It is okay. But the logic flow seems pretty complex. Can anyone translate in simple English actually what is happening?
3. I have written a function to check whether any number is prime or not. Is it okay? or I can better it by any means? function isPrime(\$num){ \$number = array(); for (\$i=2; \$i <= \$num; \$i++){ if((\$num%2)==0){ continue; } if ((\$num%\$i)==0){ break; } \$number[]=\$i; } /* * how I back calculate to make it successful foreach (\$number as \$key => \$value) { echo "\$key = \$value <br>"; } echo count(\$number); */ if (count(\$number)== (\$num-2)) { echo 'it is prime'; } else { echo 'not prime'; } } isPrime(101112345909);
4. Yes, I am agreed with Adam. To start with and getting acquainted with the MVC approach, CodeIgniter is fine. Hopefully it will catch up with the advancement taking place in the PHP world; but, till then you can start with CI.
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