Something

#include <stdio.h>

#define LOWER 0     /*xamili timi */
#define UPPER 300   /* upsiloteri timi */
#define STEP 20     /* bhma timis */

main()
{
int fahr;

for (fahr = LOWER; fahr <= UPPER; fahr = fahr+ STEP)
  printf("%3d %6.1f\n", fahr, (5.0/9.0)*(fahr-32));
}