C file input/out

[Volodya93]

Hello! I am struggling with the following question, as a beginner, I would like to ask some help if I may

"Calculate the electric current flowing through a resistor, when given the Resistance and Voltage
across the resistor. Allow the user to enter 10 sets of data, saving the values of Resistance, Voltage and Current to
file entitled "Data.txt" (using the equation = V=I*R). Then read the data from the Data.txt and display
the Power consumed by each resistor."

here is what I've done so far (doesn't work):

#include <stdio.h>
#include <stdlib.h>

int main()
{
int Resistance; int Voltage; int Current; int i;

Voltage = rand() % 100; Resistance = rand() % 50; Current = Voltage / Resistance;

FILE *fp; 
fp = fopen("data.txt","a+");

if ((fp=fopen("data.txt", "w"))==NULL) {
printf("Error opening file\n");
exit(1);
}

for (i=0;i<10;i++)
{
scanf("Enter Voltage & Resistance : %d , %d ", &Voltage, &Resistance);
fprintf(fp,"%s","%d %d %", &Voltage, &Resistance, &Current);
}

fclose(fp); 
getchar();
return 0;
}

[anduril462]

You need to explain in more detail what "doesn't work".

• Does it compile? If not, what error message(s) do you get. Copy-paste them exactly, with line numbers. Note, you should be compiling with warnings turned all the way up, and you should resolve them all, they're usually a sign of doing something wrong.
• Does it not run or crash? What output does the computer give you when it dies.
• Does it run but produce no output? Does it produce incorrect output? If incorrect, what input did you give? What output did you get and what output did you expect?

Also, in the future, please paste your code as plain text, so the forum software can add line numbers and syntax highlighting. Also, make sure your code is properly formatted and indented. This makes it easy to read, and easy for us to help you. It should look like this:

#include <stdio.h>
#include <stdlib.h>


int main()
{
    int Resistance; int Voltage; int Current; int i;


    Voltage = rand() % 100; Resistance = rand() % 50; Current = Voltage / Resistance;


    FILE *fp;
    fp = fopen("data.txt","a+");


    if ((fp=fopen("data.txt", "w"))==NULL) {
        printf("Error opening file\n");
        exit(1);
    }


    for (i=0;i<10;i++)
    {
        scanf("Enter Voltage & Resistance : %d , %d ", &Voltage, &Resistance);
        fprintf(fp,"%s","%d %d %", &Voltage, &Resistance, &Current);
    }


    fclose(fp);
    getchar();
    return 0;
}

[Adak]

First, STOP posting in anything except plain text. I can't wade through a sea of formatting junk!

Hello! I am struggling with the following question, as a beginner, I would like to ask some help if I may

here is what I've done so far (doesn't work):

#include <stdio.h>
#include <stdlib.h>

int main()
{
   int i, I, V,R;    //using V=I*R ( I=V/R )

   FILE *fp;=fopen("data.txt","w");

   if(!fp) {
      printf("Error opening file\n");
      return 1;
   }

   //get user data into the file
   for (i=0;i<10;i++) {
      printf("Enter Voltage & Resistance [V R]: ");
      fflush(stdout);
      scanf("%d  %d", &V, &R);  //use & for numbers, here
      fprintf(fp,"%d %d\n", V, R);  //no &'s here
   }
   fclose(fp);

   //now re-open that file for reading - "r" mode, read in the two 
   //values that user gave, for each of the 10 sets of data.
   //and calculate the I value, 


}

Don't add any variables you don't need. Don't change the names of the variables from what the instructions request.

Simple isn't just good in programming - it's damn near divine.

[Salem]

> fflush(stdin);
I thought better of you than to put this in your code.

> scanf("%d %d ", &V, &R); //use & for numbers, here
Beware of trailing spaces on scanf formats, they make for interesting typing experiences for users.

[Adak]

> fflush(stdin);
I thought better of you than to put this in your code.

> scanf("%d %d ", &V, &R); //use & for numbers, here
Beware of trailing spaces on scanf formats, they make for interesting typing experiences for users.

Yep, three A.M. code:

fflush(stdout); //of course

and no trailing space, for sure.

I was able just now to edit them little defects out. (Quite surprised I was under the time limit). Thanks for bringing that up, Salem.

[nonoob]

Where do you calculate the current? You should do this for each pair of voltage & current, and write out the three numbers to the file.