C语言编程深入理解取整取余取模问题示例分析

#include<stdio.h>
#include<windows.h>
int main()
{
	//本质是向0取整
   //trunc()函数也有这种作用，不过返回值是浮点数，而且必须引用math.h头文件
	int i = -2.9;
	int j = 2.9;
	printf("%d\n", i); //结果是：-2
	printf("%d\n", j); //结果是：2
	system("pause");
	return 0;
}

#include <stdio.h>
#include <math.h> //因为使用了floor函数，需要添加该头文件
#include <windows.h>
int main()
{
	//本质是向-∞取整，注意输出格式要不然看不到结果
	printf("%.1f\n", floor(-2.9)); //-3
	printf("%.1f\n", floor(-2.1)); //-3
	printf("%.1f\n", floor(2.9)); //2
	printf("%.1f\n", floor(2.1)); //2
	system("pause");
	return 0;
}

#include <stdio.h>
#include <math.h>
#include <windows.h>
int main()
{
	//本质是向+∞取整，注意输出格式要不然看不到结果
	printf("%.1f\n", ceil(-2.9)); //-2
	printf("%.1f\n", ceil(-2.1)); //-2
	printf("%.1f\n", ceil(2.9)); //3
	printf("%.1f\n", ceil(2.1)); //3
	system("pause");
	return 0;
}

#include <stdio.h>
#include <math.h>
#include <windows.h>
int main()
{
//本质是四舍五入
printf("%.1f\n", round(2.1));
printf("%.1f\n", round(2.9));
printf("%.1f\n", round(-2.1));
printf("%.1f\n", round(-2.9));
system("pause");
return 0;
}

#include <stdio.h>
#include <math.h>
#include <windows.h>
int main()
{
	const char* format = "%.1f \t%.1f \t%.1f \t%.1f \t%.1f\n";
	printf("value\tround\tfloor\tceil\ttrunc\n");
	printf("-----\t-----\t-----\t----\t-----\n");
	printf(format, 2.3, round(2.3), floor(2.3), ceil(2.3), trunc(2.3));
	printf(format, 3.8, round(3.8), floor(3.8), ceil(3.8), trunc(3.8));
	printf(format, 5.5, round(5.5), floor(5.5), ceil(5.5), trunc(5.5));
	printf(format, -2.3, round(-2.3), floor(-2.3), ceil(-2.3), trunc(-2.3));
	printf(format, -3.8, round(-3.8), floor(-3.8), ceil(-3.8), trunc(-3.8));
	printf(format, -5.5, round(-5.5), floor(-5.5), ceil(-5.5), trunc(-5.5));
	system("pause");
	return 0;
}

#include<stdio.h>
#include <windows.h>
int main()
{
	printf("%d\n", -10 / 3); //结果：-3
	printf("%d\n\n", -10 % 3); //结果：-1 为什么? -10=(-3)*3+(-1)
	printf("%d\n", 10 / -3); //结果：-3
	printf("%d\n\n", 10 % -3); //结果：1 为什么？10=(-3)*(-3)+1
	system("pause");
	return 0;
}