#include<stdio.h>
#include<math.h>

double triangleArea(int a, int b, int c);

int main()
{

    printf("請輸入三角形的三條邊長：\n");

    int a, b, c;

    scanf("%d", &a);
    scanf("%d", &b);
    scanf("%d", &c);

    double area = triangleArea(13, 14, 15);
    printf("triangle area is %f.\n", area);
    return 0;
}

double triangleArea(int a, int b, int c)
{
    double p = (a + b + c) / 2.0;

    return sqrt(p * (p - a) * (p - b) * (p - c));
}

結果如下：

請輸入三角形的三條邊長：
13
14
15
triangle area is 84.000000.
Press any key to continue

注意：輸入的三條變長要能夠組成一個三角形才可以。