#include <stdio.h>
#include <stdlib.h>

int
main(void)
{
    float new_guess;
    float last_guess;
    float number;

    printf("Enter a number: ");
    scanf("%f", &number);

    if (number < 0) {
        printf("Cannot compute the square root of a negative number !\n");
        return EXIT_FAILURE;
    }

    new_guess = 1;
    do {
        last_guess = new_guess;
        new_guess = (last_guess+number/last_guess) / 2;
        printf("%.15e\n", new_guess);
    } while (new_guess != last_guess);  //这个地方为什么能直接用!=比较两个浮点变量？

    printf("Square root of %g is %g\n", number, new_guess);

    return EXIT_SUCCESS;
}

为什么不能？！

那是条件语句啊,晕!我这个菜鸟都知道