程式碼示例：

#include <iostream>

#include <cmath>

using namespace std;

int main()

{

float a,b,c,C;

cout <<"Please enter two numbers of triangle as a and b:";

cin >> a >> b;

cout <<"Please enter the angle of the triangle as A and B:";

cin >> C;

c = sqrt(a*a + b*b - 2*a*b*cos(3.1415926/180*C));

cout <<"The length of c is:"<< c <<endl;

return 0;

}

cos接受的是弧度，輸入角度乘上pi/180轉換為弧度後呼叫才能得到正確結果