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#1
March 2nd, 2013, 04:39 PM
 l.e.a.r.n.e.r
Registered User

Join Date: Mar 2013
Posts: 1
Time spent in forums: 24 m 43 sec
Reputation Power: 0
Code is creating a read-only file. i dnt want that

#include <stdio.h>
#include<math.h>
#define e 2.7182818284590452353602874
int createfile(void)
{
FILE *Output;
Output = fopen("transient.xls", "w");
}
int data(double y,double z)
{
FILE *Output;
Output = fopen("transient.xls", "a+");
if (Output != 0)
fprintf(Output, " %lf \t %lf \n ", y,z);
else printf("file not opened");
fclose(Output);
return 0;
}
int main()
{
int x;
double v,r,l,t=0,i,a;
createfile();
printf("enter the values for voltage(in v)\n");
scanf ("%lf",&v);
printf("enter the values for resistance(in ohm) \n");
scanf ("%lf",&r);
printf("enter the values for inductance(in henry) \n");
scanf ("%lf",&l);
for (t=0;t<100;t=t+0.5)
{
a = (double)-1*l*t/r;
i = (v/r)*(1-pow(e,a));
printf(" \n the value of current is %lf", i );
data(t,i);
}
scanf ("%d",x);
return 0;
}

#2
March 3rd, 2013, 01:28 AM
 salem
Contributed User

Join Date: Jun 2005
Posts: 4,252
Time spent in forums: 2 Months 4 Weeks 1 Day 12 h 25 m 37 sec
Reputation Power: 1809
__________________
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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#3
March 3rd, 2013, 02:52 PM
 b49P23TIvg
Contributing User

Join Date: Aug 2011
Posts: 4,124
Time spent in forums: 1 Month 3 Weeks 2 Days 4 h 49 m 47 sec
Reputation Power: 455
If your file is read-only it is because of your operating system configuration. Instead, I think the actual problem is that your createfile function doesn't communicate properly with the outside world.
Code:
```/* pay attention to compiler warnings *****************/

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

/* you included math, which has M_E *****************/
#define e M_E			/* use  exp function *****************/

int createfile(void) {
/* createfile does not communicate with the outside world *****************/
FILE *Output;
Output = fopen("transient.xls", "w");
}
int data(double y,double z) {
FILE *Output;
Output = fopen("transient.xls", "a+");
if (NULL != Output)		/* NULL isn't necessarily 0 (it is in C++) *****************/
fprintf(Output, " %lf \t %lf \n ", y,z);
else fputs("file not opened",stdout);
fclose(Output);
return 0;
}
int main() {
int x;			/* x takes an unknown value *****************/
double v,r,l,t=0,i,a;
createfile();
puts("enter the values for voltage(in v)"); /* printf is inefficient.  Use it to convert values. *****************/
scanf ("%lf",&v);
puts("enter the values for resistance(in ohm)");
scanf ("%lf",&r);
puts("enter the values for inductance(in henry)");
scanf ("%lf",&l);
for (t=0;t<100;t+=0.5) {
a = (double)-1*l*t/r;
i = (v/r)*(1-pow(e,a)); 	/* you included math, use exp(a) *****************/
printf(" \n the value of current is %lf", i ); /* why do you put a space character before \n?  (at end of previous line) *****************/
data(t,i);
}
scanf ("%d",&x); /* storing an integer into unknown memory location is bad plan *****************/
/* best to fix the behavior of the console window.  Search internet for "dos window remain open" *****************/
return 0;
}```

Code:
```/* something like this */
FILE*createfile(void) {
FILE *Output;
char*filename = "transient.xls";
Output = fopen(filename, "w");
if (NULL == Output) were_totally_hosed(filename);
return Output;
}```
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