double d[7];
   d[0] = 1.1;   
   d[1] = 2.1;   
   d[2] = 3.1;
   d[3] = 4.1;   
   d[4] = 5.1;   
   d[5] = 6.1;   
   d[6] = 7.1;   
   double a,b;
   a = (d[0] d[1] d[2] d[3] d[4] d[5] d[6])/7.0;
   b=0.0;
   for(int i = 0; i < 7; i  )
      b  = d[i];
   b /= 7.0;
   if(a==b) 
      ShowMessage("True");
   else
      ShowMessage("False");       

引言: 處理double類型的資料時.常會發生計算方式不同而產生不同的結果... 例如下面程式.....

 
   double d[7];
   d[0] = 1.1;   
   d[1] = 2.1;   
   d[2] = 3.1;
   d[3] = 4.1;   
   d[4] = 5.1;   
   d[5] = 6.1;   
   d[6] = 7.1;   
   double a,b;
   a = (d[0] d[1] d[2] d[3] d[4] d[5] d[6])/7.0;
   b=0.0;
   for(int i = 0; i < 7; i  )
      b  = d[i];
   b /= 7.0;
   if(a==b) 
      ShowMessage("True");
   else
      ShowMessage("False");       

用debug看,a,b的值為 a=4.09999999999999964 b=4.10000000000000053 雖然顯示時為兩個都是4.1 但做比較時a==b,會為false.... 請問此問題大家有沒碰到?? 該如何處理,可以讓a==b為true?? 我目前是將a,b變為字串,再轉為double... sprintf(s,"%f",a); a=atof(s); 可以解決上面問題. 但有時卻會在sprintf出現Invalid floating point operation.... 而且程式會變慢.... 請問有沒其他較佳方案??? 感謝先!!

    if(  (int)((a-b)*100) == 0   )
    ....    //your code    或    #define MY_EQUAL(a,b) (int)((a-b)*100)==0