基本的函数

fabs 是计算绝对值  %lf 是代表double类型.

下面是个小例子,浮点数比较

//浮点数比较
#include <stdio.h>
#include <math.h>
int main (void){
    const double answer = 3.1415926;
    double response;
    printf("what is value of pi?\n");
    scanf("%lf",&response);
    while (fabs(response - answer) > 0.0001) {
        printf("Try again \n");
        scanf("%lf",&response);
    }
    printf("Close enough!\n");
    return 0;
}