Thread: Pointers no Pointing

Hey, still new to C and struggling in basic syntax, pointers in functions arguments keep turning up errors.

Code:

void target(&x_target_pos, &y_target_pos)

Error: ||=== Build: Debug in Graphics1 (compiler: GNU GCC Compiler) ===|
/home/user/Programming/Expo_1_Temp/src/main.c|55|error: expected declaration specifiers or ‘...’ before ‘&’ token|
/home/user/Programming/Expo_1_Temp/src/main.c|55|error: expected declaration specifiers or ‘...’ before ‘&’ token|

No, I have two functions, one gives random coordinates one uses those random coordinates to place a target in a graphics window. But I cant keep the random coordinates as a constant variable.

The problem is I have one function that should generate random coordinates and one that uses the coordinates to place a target. The reason I had to do it this way is because I have two sprites for my stickman and when he throws the target the sprites switch, to do that i have to clear the screen which means i have to get rid of the target as well. So The random coordinates have to be constant so i can replace the target at the same location that it was before the screen cleared. My syntax is just off somewhere. If there is a simpler solution I can't really see it.
Now that I've changed them to int* instead of "&" I dont get errors but that target is not placed, I think this is because the pointers hold no values? Or maybe I've made another mistake in implementation.

GFX are graphics function

Code:

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

/* globals */
/*draw stickman*/
void stickman(int user_input, int user_input_2)
{
    //head
    GFX_DrawCircle(user_input, user_input_2, 20, 2);
    //body
    GFX_DrawLine(user_input, user_input_2+20,user_input,user_input_2+70, 2);
    //arm
    GFX_DrawLine(user_input+0, user_input_2 +30,user_input-50,user_input_2+30, 2);
    //left arm holding coin
    GFX_DrawLine(user_input-50,user_input_2+30,user_input-65, user_input_2+10,2);
    //right arm holding coin
    GFX_DrawLine(user_input+0,user_input_2+30,user_input-55,user_input_2+10,2);
    //draw coin (projectile)
    GFX_DrawCircle(user_input-60,user_input_2-10,25,5);
    GFX_DrawCircle(user_input-60,user_input_2-10,15,3);
    //left leg
    GFX_DrawLine(user_input, user_input_2+70,user_input-80,user_input_2+120, 2);
    //right leg
    GFX_DrawLine(user_input, user_input_2+70,user_input+80,user_input_2+120, 2);

    GFX_UpdateDisplay();
}
/*draw stickman without coin for after projectile thrown*/
void stickman_coinless(int user_input, int user_input_2)
{
    //head
    GFX_DrawCircle(user_input, user_input_2, 20, 2);
    //body
    GFX_DrawLine(user_input, user_input_2+20,user_input,user_input_2+70, 2);
    //arm
    GFX_DrawLine(user_input, user_input_2 +30,user_input+50,user_input_2+30, 2);
    //arm
    GFX_DrawLine(user_input, user_input_2 +30,user_input-60,user_input_2-10, 2);
    //left leg
    GFX_DrawLine(user_input, user_input_2+70,user_input-80,user_input_2+120, 2);
    //right leg
    GFX_DrawLine(user_input, user_input_2+70,user_input+80,user_input_2+120, 2);

    GFX_UpdateDisplay();
}
int target_placement(int* x_target_pos, int* y_target_pos)
{
  //make random coordinates for target to appear at
    *x_target_pos = GFX_RandNumber(200, 600);
    *y_target_pos = GFX_RandNumber(1, 460);
    return 0;
}
void target(int* x_target_pos, int* y_target_pos)
{
    //draw target
    GFX_DrawCircle(x_target_pos, y_target_pos, 40, 4);
    GFX_DrawCircle(x_target_pos, y_target_pos, 30, 1);
    GFX_DrawCircle(x_target_pos, y_target_pos, 20, 4);
    GFX_DrawCircle(x_target_pos, y_target_pos, 5, 1);
    GFX_UpdateDisplay();
}

//draw projectile (coin)
int projectile(int user_input,int user_input_2,float user_input_3,float user_input_4)
{
    //set inital pos of coin
    float pos_x=user_input-60;
    float pos_y=user_input_2-10;
    //PI to a value
    int pie = 3.142;
    //move to inital
    GFX_MoveTo(pos_x, pos_y);
    //set variables
    int inital_y=pos_y;
    int inital_x=pos_x;
    float time=1;
    int gravity=9.81;
    double horiz = user_input_3*cos(user_input_4 *pie/180);
    double vertical = user_input_3*sin(user_input_4 *pie/180);
    //caculate trajectory
    while(pos_y<480)
    {
        time=(pos_x-inital_x)/horiz;
        pos_y=(inital_y)-(vertical*time)+(gravity*time*time)/2;
        GFX_DrawLineTo(pos_x,pos_y,3);

        pos_x+=1;

        printf("%f %f %f\n", pos_x, pos_y, time);

    }
    GFX_UpdateDisplay();
}

int main(void)
{
    GFX_InitWindow(640, 480);
    //white for drawing
    GFX_SetColour(RED);
    //green to symbolise start
    GFX_SetBackgroundColour(GREEN);
    GFX_UpdateDisplay();
    GFX_ClearWindow();
    //define varibale ans for user choice of carrying on
    int x_target_pos;
    int y_target_pos;
    char ans;

        //loop to ask continue
        do
        {
            printf("\nWould you like to play(Y/N)?: \n");
            scanf("%c,", &ans);
            getchar();
            GFX_SetBackgroundColour(GREEN);
            GFX_ClearWindow();
            target_placement(&x_target_pos, &y_target_pos);
            target(&x_target_pos, &y_target_pos);
            GFX_UpdateDisplay();

                //for man position
                 int user_input;
                printf("Please enter coordinate x: ");
                scanf("%d,", &user_input);
                getchar();

                int user_input_2;
                printf("Please enter coordinate y: ");
                scanf("%d,", &user_input_2);
                getchar();

                //put coin thrower down
                stickman(user_input,user_input_2);
                GFX_UpdateDisplay();

                float user_input_3;
                printf("Please specify velocity of projectile: ");
                scanf("%f,",&user_input_3);
                getchar();

                float user_input_4;
                printf("Please enter the angle: ");
                scanf("%f,",&user_input_4);
                getchar();

                //clear window and place in coinless stickman
                GFX_ClearWindow();
                stickman_coinless(user_input,user_input_2);
                target(&x_target_pos, &y_target_pos);
                projectile(user_input,user_input_2,user_input_3,user_input_4);
                GFX_SetBackgroundColour(RED);
                GFX_UpdateDisplay();
                GFX_ClearWindow();
                //ask to redo or end
                printf("\nWould you like to go again(Y/N)?: \n");
                scanf("%c",&ans);
                getchar();

                GFX_UpdateDisplay();
                } while (ans == 'y' || ans == 'Y');

                    /* Wait for a user's signal to exit*/
                    printf("Please press enter");
                    getchar();
                    getchar();

                    /* remove the display */
                    GFX_CloseWindow();

                    return 0;

    }

In target function I found that you are passing pointers instead of value. You have to dereference the pointers to the graphics functions.

what do you mean? could you give me an example?

oh yeah, but that isnt causing my current problem

made that change, now before the do loop x_target_pos=4207520 and y_target_pos=0. But after respectively 219, 47, the target still doesnt show in the graphics window though.

fyi they are supposed to be x_target_pos in range 200-400 and y_target_pos in range 1-460

Nope nvm, when calling the functions I needed to get rid of the "&"