Thread: Double

I am trying to make a program where I need to have some doubles in the read function, that needs to be used in the Tovn1 function, like ... It is double prewatt, double tovn and double maalt.

Code:

#include <stdio.h>
#include <string.h>
#include <math.h>

double Tovn1(double Tovn, double prewatt, double maalt)
{
	double P_k;
	double P_s;
	double R_th = 30;
	double C_th = 22.5;
	double A = 0.0025;
	FILE *out1;				
	out1=fopen("1output.txt","w");
	//double Tovn;
	//double prewatt = 10018.50/1000;

		P_k=(1/R_th)*(maalt-23);
		P_s=A*0.0000000567*(pow((maalt)+273,4.0)-pow(23+273,4.0));
		Tovn=maalt+(1/C_th)*(prewatt-P_k-P_s);
		printf("Tovn: %lf \t prewatt: %lf \t maalt: %lf \n", Tovn, prewatt, maalt);
		//return 0;
}

void read(int b)
{  
	int j=0;
	double i=0;
	double maalt=23;
	double prewatt=0;
	double Tovn;
	char buff[80];
	double num1, num2, num3;
	char watt[50];
	char tempmaalt[50];
	char taelle[10];
	FILE *in,*out;				
	out=fopen("output.txt","w");
	if((in=fopen("Temp.txt", "r")) == NULL) 
	{
		printf("\nError opening file");
	}
	while(fgets(buff, sizeof(buff), in))
	{
	    if (3 == sscanf(buff, "%lf %lf %lf", &num1, &num2, &num3)) 
	    {
	    	sprintf(tempmaalt, "%.1f", num2*100);
	    	sprintf(watt, "%.1f", num3*b);
	    	sprintf(taelle, "%.1f", i*0.5);
	    	j=0;
	    	while(taelle[j]!='\0')
			{
				if(taelle[j]=='.')
					taelle[j]=',';
				++j;
			}	    
	    	j=0;
	    	while(tempmaalt[j]!='\0')
	    	{
				if(tempmaalt[j]=='.')
					tempmaalt[j]=',';
				++j;
			}	    
	    	j=0;
	    	while(watt[j]!='\0')
			{
				if(watt[j]=='.')
					watt[j]=',';
				++j;
			}
	    	
	    	printf("Tidsstempel[S]: %s \t Power[W]: %s \t Measured[C]: %s \t ", taelle, watt, tempmaalt);
	        fprintf(out, "Tidsstempel[S]: %s \t Power[W]: %s \t Measured[C]: %s \t ", taelle, watt, tempmaalt);
	    	Tovn1(Tovn, prewatt, maalt);
		printf("Simulated[C]: %lf \n", Tovn);
		fprintf(out, "Simulated[C]: %lf \n", Tovn);
	    	maalt = Tovn;
	    	prewatt = num3; 
	        i++;
	    }
	}
	fclose(in);
	fclose(out);
}

void main()
{
	int a, b;
	printf("Skriv hvad du vil \n 1: Køre program \n 2: Hvis du vil ændre Volt konstanten \n");
	fflush(stdout);
	scanf("%d", &a);
	if(a==1){
		b=15;
		read(b);
	}
	else{
		printf("Skriv en Volt konstant: ");
		fflush(stdout);
		scanf("%d", &b);
		read(b);
	}
}

But I can't figure out how to make the doubles usable in other functions. Can anyone help me?

> //return 0;
Instead of this, how about

return Tovn;

You should also read this: Why void main() is bad

If you want to return multiple values from a function you need to pass in the parameters as pointers. But it seems like the Tovn1() function only changes the variable Tovn, so maybe that's the only thing you need to return. Simple example:

Code:

double sum(double x, double y, double z) {
    x += y;
    y += z;
    return x;
}

/* ... */
double q = sum(4, 5, 6);
/* ... */

Well to expand a little

Code:

	    	Tovn = Tovn1(Tovn, prewatt, maalt);
		printf("Simulated[C]: %lf \n", Tovn);
		fprintf(out, "Simulated[C]: %lf \n", Tovn);
	    	maalt = Tovn;

You should also remove these lines as well
FILE *out1;
out1=fopen("1output.txt","w");
You neither use the file, nor close it.

Originally Posted by Salem

Well to expand a little

Code:

	    	Tovn = Tovn1(Tovn, prewatt, maalt);
		printf("Simulated[C]: %lf \n", Tovn);
		fprintf(out, "Simulated[C]: %lf \n", Tovn);
	    	maalt = Tovn;

You should also remove these lines as well
FILE *out1;
out1=fopen("1output.txt","w");
You neither use the file, nor close it.

Yeah, I know. This was just a "prototype" of what I was trying to do, but I just removed the math function and integrated into the read function, which made everything easier, and now it works!

Thanks everyone and have switched to int main(void) hehe, I just went with the standard.