Comparing Floats in C: Best Practices

In C language, comparing the sizes of two floating-point numbers should be done using floating-point comparison functions such as <, >, <=, >=, ==, !=.

For example:

float a = 1.23;
float b = 4.56;

if (a < b) {
    printf("a is smaller than b\n");
} else if (a > b) {
    printf("a is larger than b\n");
} else {
    printf("a is equal to b\n");
}

It is important to note that due to precision issues with floating-point numbers, there may be some rounding errors. Therefore, when comparing floating-point numbers, one should avoid directly using the == operator. Instead, it is recommended to use a small margin of error for comparison, such as checking if the absolute difference between two floating-point numbers is less than a certain threshold.

float a = 1.2345678;
float b = 1.2345679;
float epsilon = 0.000001; // 设置一个很小的误差范围

if (fabs(a - b) < epsilon) {
    printf("a is approximately equal to b\n");
} else if (a < b) {
    printf("a is smaller than b\n");
} else {
    printf("a is larger than b\n");
}

This can prevent comparison errors caused by floating-point inaccuracies.