如何在C中将float变量与double进行比较? [英] How to compare float variable with double in C?

问题描述

float num1 = 1;

if (num1 == 1)
{
     printf("Yes, it is equal!!\n");
}
else
{
     printf("No, it is not equal\n");
}

输出->是的，它是相等的！

output --> Yes, it is equal!

而

float num1 = 1.2;

if (num1 == 1.2)
{
    printf("Yes, it is equal!!\n");
}
else
{
    printf("No, it is not equal\n");
}

输出->不，不相等

但是为什么呢?请详细说明.

but why? Please explain in detail.

推荐答案

尽管有标题，但没有与任何 int 值进行比较.

In spite of your title, there is no comparison with any int value.

num == 1.2 将 num 中的 float 值与 1.2的 double 值进行比较.

num == 1.2 compares the float value in num with the double value of 1.2.

在您的C实现中将 1.2 转换为 double 时，它将转换为最接近的可表示值.由于您的C实现将基于二进制的系统用于浮点运算，因此它不能精确表示1.2，并且转换中会出现小的错误.

When 1.2 is converted to double in your C implementation, it is converted to the nearest representable value. Since your C implementation uses a binary-based system for floating-point, it cannot exactly represent 1.2, and there is a small error in the conversion.

在 float num1 = 1.2; 中，由 1.2 产生的 double 值再次转换为 float .由于 float 的精度低于 double ，因此存在更多错误.结果是 float num1 不等于双精度 1.2 .

In float num1 = 1.2;, the double value resulting from 1.2 is converted again, this time to float. Since float has less precision than double, there is even more error. The result is that the float num1 is not equal to the double 1.2.

因此，比较 num1 == 1.2 的计算结果为false.

Thus, the comparison num1 == 1.2 evaluates to false.

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