A40 Answer

#include <stdio.h>

void circle(int radius)
{
  /* Center of the circle */
  int centRow = radius, centCol = radius;
  
  int r, c;
  const int adjust=3;
  
  for ( r=0; r<=radius*2; r+=1 )
  {
    for ( c=0; c<=radius*2; c+=1 )
      if ( (r-centRow)*(r-centRow) + (c-centCol)*(c-centCol) < radius*radius-adjust )
        putchar('*');
      else
        putchar(' ');
    putchar('\n');
  }  

}

int main(int argc, char *argv[])
{
  circle(9);  
  system("PAUSE");	
  return 0;
}

Comments: There is no need to compute square roots. Comparing the squared distances gives the same results.

The value adjust is used to make the printed circle look more like a circle than the formula gives.

The calculation could be optimized by moving part of it outside of the inner loop.