Rotation

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

void DrawRect(int x1, int y1, int x2, int y2, int x3, int y3, int x4, int y4);
void Rotate(int x1, int y1, int x2, int y2, int x3, int y3, int x4, int y4, float angle);

int main()
{
    int gd = DETECT, gm;
    int x1, y1, x2, y2, x3, y3, x4, y4;
    float angle;
    initgraph(&gd, &gm, "C:\\TURBOC3\\BGI");


    printf("Enter the 1st point for the rect (x1 y1): ");
    scanf("%d%d", &x1, &y1);

    printf("Enter the 2nd point for the rect (x2 y2): ");
    scanf("%d%d", &x2, &y2);

    printf("Enter the 3rd point for the rectangle (x3 y3): ");
    scanf("%d%d", &x3, &y3);

    printf("Enter the 4rd point for the rect (x4 y4): ");
    scanf("%d%d", &x4, &y4);

    DrawRect(x1, y1, x2, y2, x3, y3, x4, y4);

    printf("Enter the angle for rotation (in degrees): ");
    scanf("%f", &angle);

    Rotate(x1, y1, x2, y2, x3, y3,x4,y4, angle);

    getch();
    closegraph();
    return 0;
}



void DrawRect(int x1, int y1, int x2, int y2, int x3, int y3, int x4, int y4)
{
    line(x1, y1, x2, y2);
    line(x2, y2, x3, y3);
    line(x3, y3, x4, y4);
    line(x4, y4, x1, y1);   
}


void Rotate(int x1, int y1, int x2, int y2, int x3, int y3, int x4, int y4, float angle)
{
    int p = x2, q = y2;
    float radianAngle = (angle * 3.14) / 180.0;

    int a1 = p + (x1 - p) * cos(radianAngle) - (y1 - q) * sin(radianAngle);
    int b1 = q + (x1 - p) * sin(radianAngle) + (y1 - q) * cos(radianAngle);

    int a2 = p + (x2 - p) * cos(radianAngle) - (y2 - q) * sin(radianAngle);
    int b2 = q + (x2 - p) * sin(radianAngle) + (y2 - q) * cos(radianAngle);

    int a3 = p + (x3 - p) * cos(radianAngle) - (y3 - q) * sin(radianAngle);
    int b3 = q + (x3 - p) * sin(radianAngle) + (y3 - q) * cos(radianAngle);

    int a4 = p + (x4 - p) * cos(radianAngle) - (y4 - q) * sin(radianAngle);
    int b4 = q + (x4 - p) * sin(radianAngle) + (y4 - q) * cos(radianAngle);

    setcolor(1);

    DrawRect(a1, b1, a2, b2, a3, b3, a4, b4);

}