error: unable to find numeric literal operator ‘operator""M_PI’ double angle = 2M_PI/5; //五角星内角如何解决

这个错误是因为编译器无法识别 M_PI，需要在代码中包含数学库头文件 `#include <cmath>`，并确保编译器支持使用 M_PI 常量。如果仍然出现错误，可以手动定义 M_PI 常量：

#define _USE_MATH_DEFINES
#include <cmath>

const double M_PI = acos(-1.0);
double angle = 2 * M_PI / 5;

这里我们使用了 `acos(-1.0)` 来手动定义 M_PI 常量。

相关问题

task1_2.cpp: In function ‘int main()’: task1_2.cpp:7:5: error: expected ‘;’ before ‘if’ if(x<1){ ^~ task1_2.cpp:9:6: error: ‘else’ without a previous ‘if’ }else if(x>20){ ^~~~ task1_2.cpp:10:32: error: unable to find numeric literal operator ‘operator""sin’ printf("y=%f",(exp(-x)+3sin(x)+10)/(2x-1)); ^~~~ task1_2.cpp:10:45: error: unable to find numeric literal operator ‘operator""x’ printf("y=%f",(exp(-x)+3sin(x)+10)/(2x-1)); ^~ task1_2.cpp:12:28: error: unable to find numeric literal operator ‘operator""x’ printf("y=%f",sqrt(5x+3)-2);什么意思

这些错误信息是在编译task1_2.cpp文件时出现的。其中第一个错误是在if语句之前缺少了分号，需要在if语句前加上一个分号。第二个错误是else语句没有前置if语句，需要将它和上一个if语句合并为一个完整的if-else语句。第三个错误是在printf语句中使用了sin和x这两个未定义的标识符，需要在前面加上数值乘法运算符*。最后一个错误是在printf语句中使用了数字和x直接相乘但缺少了乘号*，需要在中间加上乘号。

16 15 C:\Users\86137\Desktop\未命??.cpp [Error] unable to find numeric literal operator 'operator""m'

This error message indicates that the compiler is unable to find a user-defined numeric literal operator for the 'm' suffix. This operator is typically used to define custom units of measure in C++ programs.

To resolve this error, you may need to define a numeric literal operator for the 'm' suffix in your code. This can be done using the following syntax:

constexpr long double operator"" m(long double value) {
    return value * 1000.0; // convert meters to millimeters
}

In this example, the operator converts a value in meters to millimeters. You can modify the implementation of the operator to suit your specific needs.

Once you have defined the operator, you should be able to use the 'm' suffix in your code without encountering the error message.