#include <stdio.h>
#include <math.h>
 
// Triangle構造体の定義
struct Triangle {
    double a;
    double b;
    double c;
};
 
// 三角形の面積をヘロンの公式で計算する関数
double calculate_area(struct Triangle t) {
    double s = (t.a + t.b + t.c) / 2;  // 半周長
    return sqrt(s * (s - t.a) * (s - t.b) * (s - t.c));  // 面積を計算
}
 
int main(void) {
    struct Triangle t;
 
    // ユーザが3辺の長さを入力
    scanf("%lf", &t.a); printf("a: %lf",t.a);
    scanf("%lf", &t.b); printf("b: %lf",t.b);
    scanf("%lf", &t.c); printf("c: %lf",t.c);
 
    // 面積を計算
    double area = calculate_area(t);
 
    // 結果を表示
    printf("三角形の面積は: %.5f\n", area);
 
    return 0;
}
 

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