bool is_prime(int a)
{
if(a==1){return false;}
if(a<4){return true;}
if(a%2==0){return false;}
if(a<9){return true;}
if(a%3==0){return false;}
int i;
for(i=5;(i*i)<=a;i+=6)
{
if(a%i==0){return false;}
if(a%(i+2)==0){return false;}
}
return true;
}critique welcome.
You could simplify 3-7: if(a || a<4 || !(a&1) || a<9 || !(a%3)) return(false);
would that be better?
Just easier to read.
really! you find that easier to read?
If find it easier than going through each line and staring at a solid block of text.
ok but i find following one statement after another easier than trying to evaluate 3 or 4 in one go. thanks for comments and i will keep them in mind.
You can also remove a<4 because you already have a<9.
no then line 5 would return false if a=2
i realise there is no error checking for a<1 but as the title says "simple"
no reply?
no reply?
To?
a<9 excludes all values below 9, so...
yes but 2 would be evaluated before that
/***********************************************************
if a valid prime number return true or false
***********************************************************/
int is_prime(int _iVal)
{
char bPrime;
bPrime = true;
for (int ii(2); ii < _iVal / 2; ii++)
{
if (!(_iVal % ii)){
bPrime = false;
break;
}
}
return bPrime;
}Would be better
still pretty new at this but i don't get this
char bPrime;
bPrime = true;bPrime is a bool not a char.
The return being a false or truth also means that it should be bool is_prime(...) not int is_prime(...)
is_prime(5);//returns true
is_prime(8);//returns falsechar bPrime is the returned value true or false
so you're returning a char value from an int function with a bool value?
/***********************************************************
Check to see if a valid prime number
***********************************************************/
bool is_prime(int _iVal)
{
bool bPrime;
bPrime = true;
for (int ii(2); ii < _iVal / 2; ii++)
{
if (!(_iVal % ii)){
bPrime = false;
break;
}
}
return bPrime;
}Should be thus & returns 1 or 0
Point taken I didn't write the function got off the forum sometime ago. Did not spot that nice one.
maybe just me being a noob but that looks like shit!
maybe just me being a noob but that looks like shit!
How so? It's very straightforward in fashion.
It could use a little cleaning up, but it looks fine for the most part.
ok find all the primes from 10000000-20000000 with each one and time it.
why go as far as i_Val/2?
ok find all the primes from 10000000-20000000 with each one and time it.
Why?
Title "simple prime checker" ?square root is far enough
Why?
well how else you going test it?
still waiting for a clarification on this
You can also remove a<4 because you already have a<9.
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