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Additive primes: Difference between revisions
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Found 54 additive primes < 500.</pre>
=={{header|C}}==
<lang C>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
void memoizeIsPrime( bool * result, const int N )
{
result[2] = true;
result[3] = true;
int prime[N];
prime[0] = 3;
int end = 1;
for (int n = 5; n < N; n += 2)
{
bool n_is_prime = true;
for (int i = 0; i < end; ++i)
{
const int PRIME = prime[i];
if (n % PRIME == 0)
{
n_is_prime = false;
break;
}
if (PRIME * PRIME > n)
{
break;
}
}
if (n_is_prime)
{
prime[end++] = n;
result[n] = true;
}
}
}/* memoizeIsPrime */
int sumOfDecimalDigits( int n )
{
int sum = 0;
while (n > 0)
{
sum += n % 10;
n /= 10;
}
return sum;
}/* sumOfDecimalDigits */
int main( void )
{
const int N = 500;
printf( "Rosetta Code: additive primes less than %d:\n", N );
bool is_prime[N];
memset( is_prime, 0, sizeof(is_prime) );
memoizeIsPrime( is_prime, N );
printf( " 2" );
int count = 1;
for (int i = 3; i < N; i += 2)
{
if (is_prime[i] && is_prime[sumOfDecimalDigits( i )])
{
printf( "%4d", i );
++count;
if ((count % 10) == 0)
{
printf( "\n" );
}
}
}
printf( "\nThose were %d additive primes.\n", count );
return 0;
}/* main */
</lang>
{{out}}
<pre>
Rosetta Code: additive primes less than 500:
2 3 5 7 11 23 29 41 43 47
61 67 83 89 101 113 131 137 139 151
157 173 179 191 193 197 199 223 227 229
241 263 269 281 283 311 313 317 331 337
353 359 373 379 397 401 409 421 443 449
461 463 467 487
Those were 54 additive primes.
</pre>
=={{header|C++}}==
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