Expert: Zlatko - 1/5/2012

Question
QUESTION: Hi again :)

I have encountered one final problem with another function in which I need to update my Inventory afterwards.

By default the file contains:
Total Number of Bees: 15
Total Number of Infected Bees: 5
Total Amount of Money: 1500
Total Amount of Honey Jars: 65
Total Amount of Beeswax: 0

However once I update it to increase the number of infected bees and decrease the number of total bees it just randomizes all of my numbers. Any idea how I can go around this?

Thanks :)

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

#define LINE_1 "Total Number of Bees: %d
"
#define LINE_2 "Total Number of Infected Bees: %d
"
#define LINE_3 "Total Amount of Money: %f
"
#define LINE_4 "Total Amount of Honey Jars: %d
"
#define LINE_5 "Total Amount of Beeswax: %d
"

#define FILENAME "Inventory.txt"

int main ()
{;

  int Inv_NumofBees;
  int Inv_InfectedBees;
  float Inv_Money;
  int Inv_HoneyJars;
     int Inv_Wax;

     FILE* file;

     srand (time(NULL));
     printf ("The number of bees that have been infected is %d.
", rand()%5);
     srand (1);

     file = fopen(FILENAME, "w");
        if (file == NULL)
        {
         printf("Cannot open file %s for writing
", FILENAME);
         return 0;
        }

        fprintf(file, LINE_1, Inv_NumofBees-rand);
        fprintf(file, LINE_2, Inv_InfectedBees+rand);
        fprintf(file, LINE_3, Inv_Money);
        fprintf(file, LINE_4, Inv_HoneyJars);
        fprintf(file, LINE_5, Inv_Wax);
        fclose(file);

        getchar();
        getchar();
        return 0;
  }

ANSWER: Hi Stephane

You are getting random data in the file because you are not initializing the Inv_ variables. You should always initialize all your variables before using them. Don't assume that they start at 0.

int Inv_NumofBees = 0;
int Inv_InfectedBees = 0;
float Inv_Money = 0;
int Inv_HoneyJars = 0;
int Inv_Wax = 0;

Also notice that where you are doing
Inv_NumofBees-rand

it is not calling the rand function. To call the function you need
Inv_NumofBees-rand() /* notice the parentheses () */

The value of rand is the address of the rand function in memory. The value of rand() is the value returned by the function.

Best regards
Zlatko

---------- FOLLOW-UP ----------

QUESTION: For some reason I am still getting random data in my text file despite making the adjustments. This is the current state of the program just in case.


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

#define LINE_1 "Total Number of Bees: %d\n"
#define LINE_2 "Total Number of Infected Bees: %d\n"
#define LINE_3 "Total Amount of Money: %f\n"
#define LINE_4 "Total Amount of Honey Jars: %d\n"
#define LINE_5 "Total Amount of Beeswax: %d\n"

#define FILENAME "Inventory.txt"

int main ()
{

  int Inv_NumofBees=0;
  int Inv_InfectedBees=0;
  float Inv_Money=0;
  int Inv_HoneyJars=0;
     int Inv_Wax=0;

     FILE* file;

     srand (time(NULL));
     printf ("The number of bees that have been infected is %d.\n", rand()%5);
     srand (1);

     file = fopen(FILENAME, "w");
        if (file == NULL)
        {
         printf("Cannot open file %s for writing\n", FILENAME);
         return 0;
        }

        fprintf(file, LINE_1, Inv_NumofBees-rand());
        fprintf(file, LINE_2, Inv_InfectedBees+rand());
        fprintf(file, LINE_3, Inv_Money);
        fprintf(file, LINE_4, Inv_HoneyJars);
        fprintf(file, LINE_5, Inv_Wax);
        fclose(file);

        getchar();
        getchar();
        return 0;
  }

Answer
Every time you call rand() you get a new random number. I thought that was what you wanted. I guess you actually want the same number used throughout. Of course that makes sense. Save the value like this:

int infected;
infected = rand() % 5;
Then use the infected variable instead of calling rand() in your printf, and your fprintf