[英]Rounding with c
I'm trying to convert in hours and minutes starting from times (recorded in an array) in minutes from midnight.我正在尝试从午夜开始的时间(记录在数组中)以小时和分钟为单位进行转换。 But I see that there is a rounding error.
但我看到有一个舍入错误。 For example, the departure time 583 (minutes from midnight), calculating the time and minutes like this:
例如出发时间 583(从午夜开始的分钟数),计算时间和分钟数如下:
583/60 = 9.716666 583/60 = 9.716666
I take the whole part (9) hours.我把整个部分(9)小时。 Then I take the decimal part and do this:
然后我取小数部分并这样做:
0.716666 * 60 = 42.99996 0.716666 * 60 = 42.99996
The minutes would be 43 but unfortunately I can not extrapolate this value rounding it up.分钟数为 43,但不幸的是,我无法将这个值四舍五入。
Some idea?有什么想法?
#include <stdio.h>
#define SIZE (int)sizeof(departures) / sizeof(departures[0])
int main(void) {
int hours, minutes, mmin, fh, fm;
float res;
int departures[] = {480, 583, 679, 767, 840, 945, 1140, 1305};
int Arrivals[] = {616, 712, 91, 900, 968, 1075, 1280, 1438};
for(int i = 0; i < SIZE; i++) {
res = (float)departures[i] / 60;
fh = departures[i] / 60;
fm = ((float)departures[i] / 60 - fh) * 60;
printf("%d) %d:%d (%f)\n", i, fh, fm, res);
}
return 0;
}
You can use round function:您可以使用圆形 function:
#include <stdio.h>
#include <math.h>
int main()
{
float i=5.4, j=5.6;
printf("round of %f is %f\n", i, round(i));
printf("round of %f is %f\n", j, round(j));
return 0;
}
Output: Output:
round of 5.400000 is 5.000000
5.400000 轮是 5.000000
round of 5.600000 is 6.000000
5.600000 轮是 6.000000
One doesn't need floating-point at all with the remainder %
operation.余数
%
操作根本不需要浮点数。 This is more numerically stable.这在数值上更稳定。
#include <stdio.h> /* size_t printf */
int main(void) {
unsigned departures[] = {480, 583, 679, 767, 840, 945, 1140, 1305};
const size_t departures_size = sizeof departures / sizeof *departures;
size_t i;
for(i = 0; i < departures_size; i++)
printf("%lu) %u:%u\n", (unsigned long)i,
departures[i] / 60, departures[i] % 60);
return 0;
}
I've changed the int
to unsigned int
so that one knows to not have negatives.我已将
int
更改为unsigned int
以便人们知道没有底片。 See this question for why. 请参阅此问题以了解原因。 This gives,
这给出了,
...
1) 9:43
You do the following:您执行以下操作:
583/60 = 9.716666
583/60 = 9.716666
I take the whole part (9) hours.
我把整个部分(9)小时。 Then I take the decimal part and do this:
然后我取小数部分并这样做:
0.716666 * 60 = 42.99996
0.716666 * 60 = 42.99996
Why don't you do it like this?你为什么不这样做呢?
583/60 = 9.716666 583/60 = 9.716666
You take the whole part (9) hours.你花了整个部分(9)小时。 Then you do this:
然后你这样做:
583 - (9 * 60) = 43 583 - (9 * 60) = 43
Like this, you don't need to round:-)像这样,你不需要四舍五入:-)
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