Tính diện tích và chu vi hình tam giác

//Write the program that allows the user to enter the three edges (a, b and c) of the triangle then
//calculates the perimeter and area of the triangle. The program must check that the three input
//numbers can make a triangle or not.
//Formula
//Perimeter = a + b + c
//Area = sqrt{p*(p - a)*(p - b)*(p - c)} (p = Perimeter / 2)
//Hint: use the function double sqrt (double n) of the math.h library to calculate the square root
//of the parameter n.
//Example 1: Please enter the first edge of triangle: -9
//Please enter the second edge of triangle: 7
//Please enter the third edge of triangle: 5
//These three numbers must be a positive number!
//Example 2: Please enter the first edge of triangle: 4
//Please enter the second edge of triangle: -9
//Please enter the third edge of triangle: 0
//These three numbers must be a positive number!
//Example 3: Please enter the first edge of triangle: 1
//Please enter the second edge of triangle: 2
//Please enter the third edge of triangle: 10
//These three numbers do not make a triangle!
//Example 4: Please enter the first edge of triangle: 4
//Please enter the second edge of triangle: 5
//Please enter the third edge of triangle: 6
//The perimeter of the triangle is 15
//The area of the triangle is 9.921567

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

int main() {
    int a, b, c;
    double perimeter, area, p;

    printf("Please enter the first edge of triangle: ");
    scanf("%d", &a);
    printf("Please enter the second edge of triangle: ");
    scanf("%d", &b);
    printf("Please enter the third edge of triangle: ");
    scanf("%d", &c);

    if (a <= 0 || b <= 0 || c <= 0) {
        printf("These three numbers must be a positive number!\n");
    } else if (a + b <= c || a + c <= b || b + c <= a) {
        printf("These three numbers do not make a triangle!\n");
    } else {
        perimeter = a + b + c;
        p = perimeter / 2;
        area = sqrt(p * (p - a) * (p - b) * (p - c));

        printf("The perimeter of the triangle is %.f\n", perimeter);
        printf("The area of the triangle is %.6f\n", area);
    }

    return 0;
}