c - While循环的Printf问题

Question

我正在用 C 语言创建一个温度转换器。基本上，您输入以摄氏度为单位的最小值和最大值，以及一个步骤，它会在列表中显示该信息以及等效的华氏度。在某些情况下，我注意到最后一个华氏度条目没有在应该显示的时候显示。例如，当您输入下限 10、上限 30、步长 4 时，它会截断最后的华氏温度。我知道这与最后一个 while 循环有关，但我就是想不通。

#include <stdio.h>

int main (int argc, const char * argv[]) {
double l, h, s;
double lf, hf, sf;
/* Number rows in tables */
int num1, num2;
num1 = 1;
num2 = 1;

/* Lower limit input */
printf("Please give a lower limit: ");
scanf("%4lf", &l);
while (l < 0) {
        printf("Lower limit must be greater than 0: ");
        scanf("%4lf", &l);
}

/* Stores value for Fahrenheit conversion */
lf = l;

/* Higher limit input */
printf("Please give a higher limit: ");
scanf("%4lf", &h);
while (h <= l) {
        printf("Higher limit must be greater than lower limit: ");
        scanf("%4lf", &h);
}

while (h >= 50000) {
        printf("Higher limit must be less than 50000: ");
        scanf("%4lf", &h);
}

hf = h;

/* Step input */
printf("Please input step: ");
scanf("%4lf", &s);
while (s <= 0) {
        printf("Step must be greater than 0: ");
        scanf("%4lf", &s);
}

while (s >= h - l) {
        printf("Step must be less than the difference in temperatures: ");
        scanf("%4lf", &s);
}

sf = s;

/* Celsius table */
printf("\nCelsius\n-------\n");
while (l <= h) {
    printf("%i. %4lf\n", num1, l);
    num1++;
    l = l + s;
}

/* Fahrenheit table */
printf("\nFahrenheit\n----------\n");
/* Converts Celsius to Fahrenheit */
lf = (lf * 1.8) + 32;
hf = (hf * 1.8) + 32;
sf = sf * 1.8;
printf("Lower input: %4lf\n", lf);
printf("Higher input: %4lf\n", hf);
printf("Step: %4lf\n----------\n", sf);
/* This while loop sometimes cuts off the last entry */
while (lf <= hf) {
    printf("%i. %4lf\n", num2, lf);
    num2++;
    lf = lf + sf;
}

return 0;

}

Answer 1

问题在于比较 double ，您可能​​会遇到类似 10 + 1.8 的计算结果为 11.800000001 的情况，因此会丢失最终值。

您的问题的解决方案是首先计算步数:

int steps = (h - l) / s + 1; //Might want to apply rounding

然后使用 for/while 循环遍历整数变量:

for (int i = 0; i < steps; ++i) {
    double t = l + (h - l) * i / (steps - 1);
}

for (int i = 0; i < steps; ++i) {
    double tf = lf + (hf - lf) * i / (steps - 1);
}