user-0 提问: 混合运算结果不正确

回复:
user: user-1
content: 再供参考：#include <stdio.h> #include <stdlib.h> #include <string.h> float f; double d; void showf() {     char bs[65];     char b[65];     unsigned char *p;     char e[12];     char *t;     int ex;      printf("\nf=%.6f\n",f);     p=(unsigned char *)&f;     printf("hex=%02X %02X %02X %02X\n",p[3],p[2],p[1],p[0]);     ltoa(*(long *)&f,b,2);     sprintf(bs,"%032s",b);     printf("bin=%s\n",bs);     printf("bin=%.1s %.8s   %s\n",bs,bs+1,bs+9);     strncpy(e,bs+1,8);e[8]=0;     ex=strtol(e,&t,2);     printf("    %c %-4d-127 1.%s\n",(bs[0]=='0')?'+':'-',ex,bs+9);     ex-=127;     printf("    %c %-8d 1.%s\n",(bs[0]=='0')?'+':'-',ex,bs+9); } void showd() {     char bs[65];     char b[65];     unsigned char *p;     char e[12];     char *t;     int ex;      printf("\nd=%.15lf\n",d);     p=(unsigned char *)&d;     printf("hex=%02X %02X %02X %02X %02X %02X %02X %02X\n",p[7],p[6],p[5],p[4],p[3],p[2],p[1],p[0]);     _i64toa(*(__int64 *)&d,b,2);     sprintf(bs,"%064s",b);     printf("bin=%s\n",bs);     printf("bin=%.1s %.11s   %s\n",bs,bs+1,bs+12);     strncpy(e,bs+1,11);e[11]=0;     ex=strtol(e,&t,2);     printf("    %c %-6d-1023 1.%s\n",(bs[0]=='0')?'+':'-',ex,bs+12);     ex-=1023;     printf("    %c %-11d 1.%s\n",(bs[0]=='0')?'+':'-',ex,bs+12); } int main() {      for (f=0.0f;f<=2.2f;f+=0.2f) showf();     printf("------------\n");     f=2.0f;showf();     printf("-----------------------------------\n");     for (d=0.0 ;d<=2.2 ;d+=0.2 ) showd();     printf("------------\n");     d=2.0 ;showd();      return 0; } // //f=0.000000 //hex=00 00 00 00 //bin=00000000000000000000000000000000 //bin=0 00000000   00000000000000000000000 //  + 0   -127 1.00000000000000000000000 //  + -127     1.00000000000000000000000 // //f=0.200000 //hex=3E 4C CC CD //bin=00111110010011001100110011001101 //bin=0 01111100   10011001100110011001101 //  + 124 -127 1.10011001100110011001101 //  + -3       1.10011001100110011001101 // //f=0.400000 //hex=3E CC CC CD //bin=00111110110011001100110011001101 //bin=0 01111101   10011001100110011001101 //  + 125 -127 1.10011001100110011001101 //  + -2       1.10011001100110011001101 // //f=0.600000 //hex=3F 19 99 9A //bin=00111111000110011001100110011010 //bin=0 01111110   00110011001100110011010 //  + 126 -127 1.00110011001100110011010 //  + -1       1.00110011001100110011010 // //f=0.800000 //hex=3F 4C CC CD //bin=00111111010011001100110011001101 //bin=0 01111110   10011001100110011001101 //  + 126 -127 1.10011001100110011001101 //  + -1       1.10011001100110011001101 // //f=1.000000 //hex=3F 80 00 00 //bin=00111111100000000000000000000000 //bin=0 01111111   00000000000000000000000 //  + 127 -127 1.00000000000000000000000 //  + 0        1.00000000000000000000000 // //f=1.200000 //hex=3F 99 99 9A //bin=00111111100110011001100110011010 //bin=0 01111111   00110011001100110011010 //  + 127 -127 1.00110011001100110011010 //  + 0        1.00110011001100110011010 // //f=1.400000 //hex=3F B3 33 34 //bin=00111111101100110011001100110100 //bin=0 01111111   01100110011001100110100 //  + 127 -127 1.01100110011001100110100 //  + 0        1.01100110011001100110100 // //f=1.600000 //hex=3F CC CC CE //bin=00111111110011001100110011001110 //bin=0 01111111   10011001100110011001110 //  + 127 -127 1.10011001100110011001110 //  + 0        1.10011001100110011001110 // //f=1.800000 //hex=3F E6 66 68 //bin=00111111111001100110011001101000 //bin=0 01111111   11001100110011001101000 //  + 127 -127 1.11001100110011001101000 //  + 0        1.11001100110011001101000 // //f=2.000000 //hex=40 00 00 01 //bin=01000000000000000000000000000001 //bin=0 10000000   00000000000000000000001 //  + 128 -127 1.00000000000000000000001 //  + 1        1.00000000000000000000001 //------------ // //f=2.000000 //hex=40 00 00 00 //bin=01000000000000000000000000000000 //bin=0 10000000   00000000000000000000000 //  + 128 -127 1.00000000000000000000000 //  + 1        1.00000000000000000000000 //----------------------------------- // //d=0.000000000000000 //hex=00 00 00 00 00 00 00 00 //bin=0000000000000000000000000000000000000000000000000000000000000000 //bin=0 00000000000   0000000000000000000000000000000000000000000000000000 //  + 0     -1023 1.0000000000000000000000000000000000000000000000000000 //  + -1023       1.0000000000000000000000000000000000000000000000000000 // //d=0.200000000000000 //hex=3F C9 99 99 99 99 99 9A //bin=0011111111001001100110011001100110011001100110011001100110011010 //bin=0 01111111100   1001100110011001100110011001100110011001100110011010 //  + 1020  -1023 1.1001100110011001100110011001100110011001100110011010 //  + -3          1.1001100110011001100110011001100110011001100110011010 // //d=0.400000000000000 //hex=3F D9 99 99 99 99 99 9A //bin=0011111111011001100110011001100110011001100110011001100110011010 //bin=0 01111111101   1001100110011001100110011001100110011001100110011010 //  + 1021  -1023 1.1001100110011001100110011001100110011001100110011010 //  + -2          1.1001100110011001100110011001100110011001100110011010 // //d=0.600000000000000 //hex=3F E3 33 33 33 33 33 34 //bin=0011111111100011001100110011001100110011001100110011001100110100 //bin=0 01111111110   0011001100110011001100110011001100110011001100110100 //  + 1022  -1023 1.0011001100110011001100110011001100110011001100110100 //  + -1          1.0011001100110011001100110011001100110011001100110100 // //d=0.800000000000000 //hex=3F E9 99 99 99 99 99 9A //bin=0011111111101001100110011001100110011001100110011001100110011010 //bin=0 01111111110   1001100110011001100110011001100110011001100110011010 //  + 1022  -1023 1.1001100110011001100110011001100110011001100110011010 //  + -1          1.1001100110011001100110011001100110011001100110011010 // //d=1.000000000000000 //hex=3F F0 00 00 00 00 00 00 //bin=0011111111110000000000000000000000000000000000000000000000000000 //bin=0 01111111111   0000000000000000000000000000000000000000000000000000 //  + 1023  -1023 1.0000000000000000000000000000000000000000000000000000 //  + 0           1.0000000000000000000000000000000000000000000000000000 // //d=1.200000000000000 //hex=3F F3 33 33 33 33 33 33 //bin=0011111111110011001100110011001100110011001100110011001100110011 //bin=0 01111111111   0011001100110011001100110011001100110011001100110011 //  + 1023  -1023 1.0011001100110011001100110011001100110011001100110011 //  + 0           1.0011001100110011001100110011001100110011001100110011 // //d=1.400000000000000 //hex=3F F6 66 66 66 66 66 66 //bin=0011111111110110011001100110011001100110011001100110011001100110 //bin=0 01111111111   0110011001100110011001100110011001100110011001100110 //  + 1023  -1023 1.0110011001100110011001100110011001100110011001100110 //  + 0           1.0110011001100110011001100110011001100110011001100110 // //d=1.600000000000000 //hex=3F F9 99 99 99 99 99 99 //bin=0011111111111001100110011001100110011001100110011001100110011001 //bin=0 01111111111   1001100110011001100110011001100110011001100110011001 //  + 1023  -1023 1.1001100110011001100110011001100110011001100110011001 //  + 0           1.1001100110011001100110011001100110011001100110011001 // //d=1.800000000000000 //hex=3F FC CC CC CC CC CC CC //bin=0011111111111100110011001100110011001100110011001100110011001100 //bin=0 01111111111   1100110011001100110011001100110011001100110011001100 //  + 1023  -1023 1.1100110011001100110011001100110011001100110011001100 //  + 0           1.1100110011001100110011001100110011001100110011001100 // //d=2.000000000000000 //hex=3F FF FF FF FF FF FF FF //bin=0011111111111111111111111111111111111111111111111111111111111111 //bin=0 01111111111   1111111111111111111111111111111111111111111111111111 //  + 1023  -1023 1.1111111111111111111111111111111111111111111111111111 //  + 0           1.1111111111111111111111111111111111111111111111111111 // //d=2.200000000000000 //hex=40 01 99 99 99 99 99 99 //bin=0100000000000001100110011001100110011001100110011001100110011001 //bin=0 10000000000   0001100110011001100110011001100110011001100110011001 //  + 1024  -1023 1.0001100110011001100110011001100110011001100110011001 //  + 1           1.0001100110011001100110011001100110011001100110011001 //------------ // //d=2.000000000000000 //hex=40 00 00 00 00 00 00 00 //bin=0100000000000000000000000000000000000000000000000000000000000000 //bin=0 10000000000   0000000000000000000000000000000000000000000000000000 //  + 1024  -1023 1.0000000000000000000000000000000000000000000000000000 //  + 1           1.0000000000000000000000000000000000000000000000000000 //

user: user-1
content: 引用 11 楼 qq_37867710 的回复:引用 10 楼 zhao4zhong1 的回复:浮点数格式 http://bbs.csdn.net/topics/390676437那个，，，老师，我还是新手，，，有些看不懂 因为一旦你看懂了这个，你就再也不会对浮点数在计算机中的表示和计算精度相关问题云里雾里了， 所以你现在必须把全部时间和精力用来看懂这个。

user: user-2
content: 引用 12 楼 qq_37867710 的回复:[quote=引用 9 楼 shihengzhen101 的回复:] [quote=引用 8 楼 qq_37867710 的回复:] [quote=引用 6 楼 shihengzhen101 的回复:]  这个是32位编译器编译运行的结果  这个是64位编译器编译运行的结果  两次都是使用VS2008，说明和编译器也是有点关系的那么这是什么原因呢，看其他人一样的程序结果是正确的，那为什么同样的程序32位与64位结果会有区别呢？[/quote] 我的测试结果也是对的啊，只不过不同位数结果的精度不同，但是不像你的结果偏差那么大！！！[/quote]而且我不论是64位还是32位结果都一样，，，都不精确，我的是vs17，不知道怎么回事[/quote] 还是应该按照正常的计算方式计算，计算整数和浮点数相加，应该先把整数转换成浮点数，相加后输出结果时，输出的格式符应该与输出类型相匹配，如果做到这样，那么误差应该就很小了，你可以试试

user: user-0
content: 引用 9 楼 shihengzhen101 的回复:[quote=引用 8 楼 qq_37867710 的回复:] [quote=引用 6 楼 shihengzhen101 的回复:]  这个是32位编译器编译运行的结果  这个是64位编译器编译运行的结果  两次都是使用VS2008，说明和编译器也是有点关系的那么这是什么原因呢，看其他人一样的程序结果是正确的，那为什么同样的程序32位与64位结果会有区别呢？[/quote] 我的测试结果也是对的啊，只不过不同位数结果的精度不同，但是不像你的结果偏差那么大！！！[/quote]而且我不论是64位还是32位结果都一样，，，都不精确，我的是vs17，不知道怎么回事

user: user-0
content: 引用 10 楼 zhao4zhong1 的回复:浮点数格式 http://bbs.csdn.net/topics/390676437那个，，，老师，我还是新手，，，有些看不懂

user: user-1
content: 浮点数格式 http://bbs.csdn.net/topics/390676437

user: user-2
content: 引用 8 楼 qq_37867710 的回复:[quote=引用 6 楼 shihengzhen101 的回复:]  这个是32位编译器编译运行的结果  这个是64位编译器编译运行的结果  两次都是使用VS2008，说明和编译器也是有点关系的那么这是什么原因呢，看其他人一样的程序结果是正确的，那为什么同样的程序32位与64位结果会有区别呢？[/quote] 我的测试结果也是对的啊，只不过不同位数结果的精度不同，但是不像你的结果偏差那么大！！！

user: user-0
content: 引用 6 楼 shihengzhen101 的回复: 这个是32位编译器编译运行的结果  这个是64位编译器编译运行的结果  两次都是使用VS2008，说明和编译器也是有点关系的那么这是什么原因呢，看其他人一样的程序结果是正确的，那为什么同样的程序32位与64位结果会有区别呢？

user: user-1
content: 浮点数格式 http://bbs.csdn.net/topics/390676437

user: user-2
content: 这个是32位编译器编译运行的结果  这个是64位编译器编译运行的结果  两次都是使用VS2008，说明和编译器也是有点关系的

user: user-3
content: http://blog.csdn.net/cookie_234/article/details/70904152 https://zh.wikipedia.org/wiki/IEEE_754 楼主不妨看看上面链接，看看32位（float）和64位（double）浮点数的具体标准

user: user-4
content: double精度比float高 所以比较准确

user: user-0
content: 引用 1 楼 mstlq 的回复:http://c.biancheng.net/cpp/html/21.html 看看类似上面的文章，或者google "浮点数 精度"没太懂，我把float更改成double就能正确得到结果

user: user-0
content: 但是float更换成double就能得到正确结果啊

user: user-3
content: http://c.biancheng.net/cpp/html/21.html 看看类似上面的文章，或者google "浮点数 精度"