加载中…C++判断整数是否为偶数的两种方法
(2019-03-18 10:38:24)
标签：
判断偶数 |
方法1：采用求余方法%
int a = 100;
bool b;
b = (a%2 ==0);
方法2：采用位逻辑符号&
int a = 100;
bool b;
b = !(a&1); // 注意要取反
到底哪个速度快？
#include "stdlib.h" // CPU 端分配内存给变量，显示不出<>，用引号替代
#include "stdio.h" // printf
#include "time.h" //clock_t
#include "chrono"
using namespace std; // 必要，放在前
using namespace chrono; // 必要
int main()
{
int n = 200000;
int a[200000];
bool b[200000];
for (int i = 0; i < n; i++)
a[i] = i;
for (int i = 0; i < n; i++)
b[i] = true;
auto start = system_clock::now();
for (int i = 0; i < n; i++)
b[i] = (a[i] % 2 == 0);
auto end = system_clock::now();
auto duration = duration_cast(end - start);
printf("(CPU) cost time: %f ms\n", 1000 *
double(duration.count())*microseconds::period::num /
microseconds::period::den);
start = system_clock::now();
for (int i = 0; i < n; i++)
b[i] = !(a[i] & 1);
end = system_clock::now();
duration = duration_cast(end - start);
printf("(CPU) cost time: %f ms\n", 1000 *
double(duration.count())*microseconds::period::num /
microseconds::period::den);
return 0;
}
自己测完就清楚了。
喜欢
0
赠金笔