Thread: First time using pointers, and i feel lost :|

It's me again, trying to figure out how to use pointers,
Im supposed to calculate alpha, beta and the lenght of c of a trianlge using a function (triangle_1)
and from what i think i'll have to use *pointers to get the values out of the function.
i tested the *cc, *alpha and *beta calculations outside a function and they seem to work

Code:

#include <stdio.h>#include <math.h>
#define TOTAL_DEG  (180.0)


void triangle_1 (double a, double b,double c, double gamma, double *cc, double *alpha, double *beta)
    {
        
        *cc= sqrt((a*a+b*b-(2*a*b*cos(gamma))));
        *alpha =(gamma)*(acos((double)(b*b +(c)*(c)- a*a)/(2.0*b*c)));
        *beta = -gamma-*alpha+TOTAL_DEG;
        
    }    
        
        
int main()
{
    double a,b,c,gamma,alpha,beta,result;
    double tri;
    printf("Bitte gib a, b und gamma eines Dreiecks ein\n");
    scanf("%lf,%lf,%lf",&a,&b,&gamma);
    prinf("a,b,c: %lf %lf %lf; gegenueber liegende Winkel: %lf %lf %lf",a,b,c,*alpha,*beta,gamma);
    
    return 0;
    
    
}
    
    
}

thanks for the help o/


*edit, im unsure if im missing these to get the rad to degree or the other way around, i always hated trigonometry
double rad (double grad) {return (grad/45.) * atan(1.);}
double grad (double rad) {return (rad*45.) / atan(1.);}

Recall that given a double variable named alpha, to get a pointer to alpha, you should use the address-of operator &, not the dereference operator, i.e., &alpha

By the way, triangle_1 is a rather poor name for a function. You probably have no choice in the matter, but it would be better design to have three functions:

Code:

double compute_length_of_third_side(double a, double b, double gamma)
{
    return sqrt(a * a + b * b - (2 * a * b * cos(gamma)));
}

double compute_alpha(double a, double b, double c, double gamma)
{
    return gamma * acos((double)(b * b + c * c - a * a) / (2.0 * b * c));
}

double compute_beta(double gamma, double alpha)
{
    return -gamma - alpha + TOTAL_DEG;
}

Notice that this reveals a problem with your triangle_1 function: you don't need c because you're computing it, and subsequently your use of c without overwriting it is a bug.

Code:

#include <stdio.h>#include <math.h>
#include <stdlib.h>
#define TOTAL_DEG  (180.0)


double berechnung_length(double a, double b, double gamma, double c)
{	
    c = sqrt(a * a + b * b - (2 * a * b * cos(gamma)));
	return c;
}
 
double berechnung_alpha(double a, double b, double c, double gamma, double alpha)
{
	alpha = gamma * acos((double)(b * b + c * c - a * a) / (2.0 * b * c));
    return alpha;
}
 
double berechnung_beta(double gamma, double alpha, double beta)
{
	beta = - gamma - alpha + TOTAL_DEG;
     return beta;
}


//void triangle_1 (double a, double b,double c, double gamma, double *cc, double *alpha, double *beta)
//	{
//		
//		*cc= sqrt((a*a+b*b-(2*a*b*cos(gamma))));
//		*alpha =(gamma)*(acos((double)(b*b +(c)*(c)- a*a)/(2.0*b*c)));
//		*beta = -gamma-*alpha+TOTAL_DEG;
//		
//	}	
		
		
int main()
{
	double a,b,c,gamma;
	double laenge, alpha, beta;
	
	printf("Bitte gib a, b und gamma eines Dreiecks ein\n");
	scanf("%lf %lf %lf",&a,&b,&gamma);
	laenge = berechnung_length(a,b,gamma, c);
	alpha = berechnung_alpha(a,b,c,gamma, alpha);
	printf("a = %lf\t b = %lf\t gamma = %lf \t",a,b,gamma);
	printf("Daraus folgt c = %lf, alpha = %lf und beta = %lf", laenge, alpha, beta);
	return 0;
	
	
}

so i changed it up a bit, left my old weird stuff in with the //'s
seems to kinda be working now, but idk if its my fault but it keeps returning -1.#IND00 or 0.00000 as the calculation
*edit the c calculation is working

Don't use function parameters as local variables!
And you never call berechnung_beta.

Code:

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
 
#define TOTAL_DEG 180.0
 
double berechnung_length(double a, double b, double gamma)
{   
    return sqrt(a * a + b * b - (2 * a * b * cos(gamma)));
}
  
double berechnung_alpha(double a, double b, double c, double gamma)
{
    return gamma * acos((double)(b * b + c * c - a * a) / (2.0 * b * c));;
}
 
double berechnung_beta(double gamma, double alpha)
{
    return -gamma - alpha + TOTAL_DEG;
}
 
int main()
{
    double a, b, gamma;
    printf("Bitte gib a, b und gamma eines Dreiecks ein\n");
    scanf("%lf %lf %lf",&a,&b,&gamma);
 
    double laenge = berechnung_length(a,b,gamma);
    double alpha = berechnung_alpha(a,b,laenge,gamma);
    double beta = berechnung_beta(gamma, alpha);
 
    printf("a = %lf\t b = %lf\t gamma = %lf\n",a,b,gamma);
    printf("Daraus folgt c = %lf, alpha = %lf und beta = %lf\n",
        laenge, alpha, beta);
}

If it still gives wrong answers, you need to tell us what inputs you are using and what output you expected.