Thread: Homework Help URGENT

> ROCKET selectRocket(ROCKET *rockets, int selection)
You need to make this return either the selection, or the rocket.
At the moment, it's doing neither.

> selection= &rockets;
If your compiler isn't giving you a warning about this, then you need to upgrade.

main returns int, not void.

it does give me an error and i removed it since it really didn't change anything , however even after making selectRocket return selection my program is still shutting down everytime before returning v.I also fixed the types considering it will be return an integer

Well you need to post your latest code if you're still stuck.

this might help, it gets you a return so you can know which rocket to work on.

Code:

#include <stdio.h>
#include <math.h>
#define G 9.81 // m/s

/**
 * The user is supposed to make a selection of an element in the array(whether Rocket 1 , Rocket 2 ,...)
 * then use that selection to access the element of the array with the data (u,m0,...) and use it in my calculation.

However, program shuts down after i enter the time.

I don't know what's going on I mean i am trying to make the "selection"
* a number of an array so that in computeSpeed it can be used to indicate which element the user selected
***/

typedef struct
{
  char* name;
  double u;
  double m0;
  double q;
}ROCKET;


    int selectRocket(ROCKET rockets[]);
    double computeSpeed(double t , ROCKET *rockets, int selection);

int main()
{
    double t;
    double v;
    int sel;

    ROCKET rockets[4]= {
             {"Rocket 1", 2000.0, 150000.0, 2700.0},
             {"Rocket 2", 1596.0, 300000.0, 5367.0},
             {"Rocket 3", 3267.0, 543135.0, 8900.0},
             {"Rocket 4", 984.0, 5468.0, 89.5}
 };

    sel =  selectRocket(rockets);
    printf("s = %d selection is = %s %f  %f  %f\n", sel, rockets[sel].name, rockets[sel].u,rockets[sel].m0,rockets[sel].q);

    // v = computeSpeed (t, rockets,selection);
    //  printf(" v =%lf ",v);
return 0;
}

int selectRocket(ROCKET rockets[])
{
 int s;

printf("%s : u = %.2lf m0 = %.2lf q = %.2lf \n", rockets[0].name ,rockets[0].u,rockets[0].m0,rockets[0].q);
printf("%s : u = %.2lf m0 = %.2lf q = %.2lf \n", rockets[1].name ,rockets[1].u,rockets[1].m0,rockets[1].q);
printf("%s : u = %.2lf m0 = %.2lf q = %.2lf \n", rockets[2].name ,rockets[2].u,rockets[2].m0,rockets[2].q);
printf("%s : u = %.2lf  m0 = %.2lf   q = %.2lf \n", rockets[3].name ,rockets[3].u,rockets[3].m0,rockets[3].q);


printf("Please select a rocket (1 to 4): ");
scanf("%d",&s);

//to compensate for zero base array.
return ( s - 1 );

}
double computeSpeed(double t , ROCKET *rockets, int selection)
{
    double v;
    // no math computations ??
   v = rockets[selection].q;
   return v;
}

Results:

Code:

[userx@void bin]$ ./a.out
Rocket 1 : u = 2000.00 m0 = 150000.00 q = 2700.00
Rocket 2 : u = 1596.00 m0 = 300000.00 q = 5367.00
Rocket 3 : u = 3267.00 m0 = 543135.00 q = 8900.00
Rocket 4 : u = 984.00  m0 = 5468.00   q = 89.50
Please select a rocket (1 to 4): 3

s = 2 selection is = Rocket 3 3267.000000  543135.000000  8900.000000

[userx@void bin]$ ./a.out
Rocket 1 : u = 2000.00 m0 = 150000.00 q = 2700.00
Rocket 2 : u = 1596.00 m0 = 300000.00 q = 5367.00
Rocket 3 : u = 3267.00 m0 = 543135.00 q = 8900.00
Rocket 4 : u = 984.00  m0 = 5468.00   q = 89.50
Please select a rocket (1 to 4): 4

s = 3 selection is = Rocket 4 984.000000  5468.000000  89.500000

Originally Posted by Kamal Joub

you were very helpful , i finished the homework thanks to you , the problem was i didnt not assign the selected value by the user to anything so when you used the "sel=" it kinda fixed the problem , also the fact that it's a zero base array and i needed to return a "s-1"helped because i kept getting the element in the array that was after the one chosen.

btw FYI ,i do have math calculations but that wasn't the problem so i just used a "dummy equation" as a test.

thank you very much for your help and just a quick question , in the protypes you used " intselectRocket(ROCKET rockets[]) " were the brackets after rockets to indicate that its an array ?

Yes

as well as adding more variables to be passed within the function. as you should have noticed the differences in that too with your functions and the ones I redid for you. also a different means of returning a value instead of adding it to a variable first then returning that just do it like how your computeSpeed is returning it : it saves on memory usage and time to execute the function.

and you're welcomed, happy to have helped.