C语言基础浮点数问题

为什么运行一下代码结果是无线循环。

```c
#include <stdio.h>
int main()
{
    double i ;
    for(i = 0; i != 10; i += 0.1)
        printf("%.1f\n", i); 
    
    return 0;
}

即使将i！=10改成i！=10.0也是无限循环。
怎样修改才能让其增加到10退出循环呢。

浮点型精度的运算是不准确的，你这里看小数点后一位是看不出来的，可以打印十几位看看。
所以当i加到10的时候并不是10，小数点后还是有值的。所以这里会进入死循环。
所以开发中是要避免使用浮点型数值做精准判断的。
你可以这么修改打印看一下运行结果：

double i ;
for(i = 0; i != 10; i += 0.1) {
    
    printf("%.16lf\n", i);
    if (i > 20) {
        
        break;
    }
}

增加到10,就退出，其实就是i大于等于10就退出啊，改成i<=10就行了啊

二进制浮点数无法精确标示十进制

仅供参考：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
    float f;
    double d;
    char bs[65];
    char b[65];
    char s[80];
    unsigned char *p;
    char e[12];
    char *t;
    int ex;
    int flag;

    flag=0;
    while (1) {
        printf("Input a float point number or 0xXXXXXXXX or 0xXXXXXXXXXXXXXXXX:");fflush(stdout);
        rewind(stdin);
        fgets(s,80,stdin);
        if ('\n'==s[0]) return 1;
        if (1==sscanf(s,"0x%16I64X",(__int64 *)&d) && strlen(s)>11) {flag=2;break;}
        if (1==sscanf(s,"0x%8X"    ,(  int   *)&f))                 {flag=1;break;}
        if (1==sscanf(s,"%f"       ,           &f)
         && 1==sscanf(s,"%lf"      ,           &d))                 {flag=3;break;}
    }
    if (flag&1) {
        printf("f=%g\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);
    }
    if (flag&2) {
        printf("\nd=%lg\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);
    }

    return 0;
}
//Input a float point number or 0xXXXXXXXX or 0xXXXXXXXXXXXXXXXX:0x3FC0000000000000
//
//d=0.125
//hex=3F C0 00 00 00 00 00 00
//bin=0011111111000000000000000000000000000000000000000000000000000000
//bin=0 01111111100   0000000000000000000000000000000000000000000000000000
//    + 1020  -1023 1.0000000000000000000000000000000000000000000000000000
//    + -3          1.0000000000000000000000000000000000000000000000000000
//
//Input a float point number or 0xXXXXXXXX or 0xXXXXXXXXXXXXXXXX:0x3E000000
//
//f=0.125
//hex=3E 00 00 00
//bin=00111110000000000000000000000000
//bin=0 01111100   00000000000000000000000
//    + 124 -127 1.00000000000000000000000
//    + -3       1.00000000000000000000000
//
//Input a float point number or 0xXXXXXXXX or 0xXXXXXXXXXXXXXXXX:0.125
//f=0.125
//hex=3E 00 00 00
//bin=00111110000000000000000000000000
//bin=0 01111100   00000000000000000000000
//    + 124 -127 1.00000000000000000000000
//    + -3       1.00000000000000000000000
//
//d=0.125
//hex=3F C0 00 00 00 00 00 00
//bin=0011111111000000000000000000000000000000000000000000000000000000
//bin=0 01111111100   0000000000000000000000000000000000000000000000000000
//    + 1020  -1023 1.0000000000000000000000000000000000000000000000000000
//    + -3          1.0000000000000000000000000000000000000000000000000000
//
//Input a float point number or 0xXXXXXXXX or 0xXXXXXXXXXXXXXXXX:
//