C ++中的atan()函数以弧度形式返回数字（参数）的反正切值。
此函数在<cmath>头文件中定义。
[数学] tan-1x = atan(x) [C++];
double atan(double x); float atan(float x); long double atan(long double x); double atan (T x); //为整型
atan()函数采用一个强制性参数（可以为正，负或零）
atan()函数返回[-π/ 2，π/ 2]范围内的值。
#include <iostream>
#include <cmath>
using namespace std;
int main()
{
double x = 57.74, result;
result = atan(x);
cout << "atan(x) = " << result << " radians" << endl;
//输出度数
cout << "atan(x) = " << result*180/3.1415 << " degrees" << endl;
return 0;
}运行该程序时，输出为：
atan(x) = 1.55348 radians atan(x) = 89.0104 degrees
#include <iostream>
#include <cmath>
#define PI 3.141592654
using namespace std;
int main()
{
int x = 14;
double result;
result = atan(x);
cout << "atan(x) = " << result << " radians" << endl;
//输出度数
cout << "atan(x) = " << result*180/3.1415 << " degrees" << endl;
return 0;
}运行该程序时，输出为：
atan(x) = 1.49949 radians atan(x) = 85.9169 degrees