Data commit

Task/Additive-primes/Free-Pascal/additive-primes.pas

@@ -0,0 +1,61 @@
+Program AdditivePrimes;
+Const max_number = 500;
+
+Var is_prime : array Of Boolean;
+
+Procedure sieve(Var arr: Array Of boolean );
+{use Sieve of Eratosthenes to find all primes to max number}
+Var i,j : NativeUInt;
+
+Begin
+  For i := 2 To high(arr) Do
+    arr[i] := True;  // set all bits to be True
+  For i := 2 To high(arr) Do
+    Begin
+      If (arr[i]) Then
+        For j := 2 To (high(arr) Div i) Do
+          arr[i * j] := False;
+    End;
+End;
+
+Function GetSumOfDigits(num: NativeUInt): longint;
+{calcualte the sum of digits of a number}
+Var
+  sum  : longint = 0;
+  dummy: NativeUInt;
+Begin
+  Repeat
+    dummy := num;
+    num := num Div 10;
+    Inc(sum, dummy - (num SHL 3 + num SHL 1));
+  Until num < 1;
+  GetSumOfDigits := sum;
+End;
+
+Var x : NativeUInt = 2; {first prime}
+  counter : longint = 0;
+Begin
+  setlength(is_prime,max_number); //set length of array to max_number
+  Sieve(is_prime); //apply Sieve
+
+  {since 2 is the only even prime, let's do it separate}
+  If is_prime[x] And is_prime[GetSumOfDigits(x)] Then
+    Begin
+      write(x:4);
+      inc(counter);
+    End;
+  inc(x);
+  While x < max_number Do
+    Begin
+      If is_prime[x] And is_prime[GetSumOfDigits(x)] Then
+        Begin
+          if counter mod 10 = 0 then writeln();
+          write(x:4);
+          inc(counter);
+        End;
+      inc(x,2);
+    End;
+  writeln();
+  writeln();
+  writeln(counter,' additive primes found.');
+End.