/* ---------------------------------------------------------------------  
//  Figure 7.28:  A projectile.
//                Mixing floats and doubles in a computation.             
// --------------------------------------------------------------------- 
*/
#include "tools.h"  

void main( void )                                                              
{ 
    int alpha;              /* angle of ball from horizontal      */  
    float vel_o;            /* initial velocity in m/s            */    
    float x;                /* horizontal dimension of travel     */    
    double vx, vy;          /* x and y components of velocity     */    
    double a_rad;           /* angle alpha, in radians            */    
    double t;               /* time in seconds for ball to hit ground */

    banner();
    printf( "\n Enter the initial velocity (m/s):  " );     
    scanf( "%g", &vel_o );                                   
    printf( " Enter firing angle from the horizontal, in degrees:  " );
    scanf( "%i", &alpha );
 
    if (alpha < 0 || alpha > 90)        /* check for bad firing angle */  
        printf( "Error: Firing angle must be in range 0...90 degrees." ); 
    else if (vel_o < 0 || vel_o > 100)  /* check for bad velocity */ 
        printf( "Error: Initial velocity must be in range 0...100 m/s." );  
    else {                              /* inputs are valid */  
        a_rad = alpha * PI / 180.;      /* convert angle to radians. */
        vx = vel_o * cos( a_rad );                                        
        vy = vel_o * sin( a_rad ); 

        t = 2 * vy / GRAVITY;           /* time of fall */                       
        x = vx * t;                     /* distance of travel  */
                
        printf( "\n For initial velocity = %.3f m/s"               
                "\n    and angle from the horizontal = %i degrees"  
                "\n    The ball travels %.3f meters \n",  vel_o, alpha, x );
        bye();
    }
 }