Creating a file with random numbers question??

Hey guys. I need some help..bad. I have to write a program that creates a file of randomly distributed numbers. I have the functions figured out and some of the main(). Could you guys take a look at it and just try to steer me in the right direction. I'm just confused on how to get a filename from user, and how many numbers they want to see, then acutally do it. I just need some help getting started.

Heres the code:

Code:

---

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

void get_info(char *filename, int *n_ptr);

FILE *cfopen(char *filename, char *mode);

FILE *gfopen(char *filename, char *mode);

int main( int argc, char **argv)
{
      FILE  *ofp;
      int      i;

      // I don't know if I've declared all that I should, and I'm not
      // sure how to call the functions.



      for(i=1; i<=n; ++i){
          fprintf(ofp, "%12d", rand());
          if(i%6 == 0 || i == n)
              fprintf(ofp, "\n");
}


void get_info(char *filename, int *n_ptr)
{
    prinf("\n%S\n\n%s",
        "This progam creates a file of random numbers.",
        "How many random numbers would you like?  "),
    scanf("%d", n_ptr);
    printf("\nIn what file would you like them?  ");
    scanf("%s", filename);
}




FILE *cfopen(char *filename, char *mode)
{
    char  reply[2];
    FILE  *fp;
 
    if(strcmp(mode, "w") == 0
      && (fp = fopen(filename, "r")) != NULL){
        fclose(fp);
        printf("\nFile exists.  Overwrite it? ");
        scanf("%1s", reply);
        if(*reply != 'y' && *reply != 'Y') {
        printf("\nBye!\n\n");
        exit(1);
        }
      fp = gfopen(filename, mode);
      return fp;
}



FILE *gfopen(char *filename, char *mode)
{
    FILE *fp;
   
    if((fp = fopen(filename,mode)) == NULL){
    fprintf(stderr, "Cannot open %s - bye!\n", filename); 
    exit(1);
    }
    return fp;
}

---

Any help would be greatly appreciated!!!!!

okay, I just realized that I don't need to use argc and argv in this, but I still am not sure what all I have to Initialize and then pass to the funtions. I think I have to include an array so that the numbers will be printed by the fprintf statements, but I'm not sure how to set that up either. Any advice - just advice?

first things first, you need to learn how to generate a good set of
random numbers. you need to seed rand first like this:

Code:

---

#include <time.h>

int main (void)
{
      int i, j, k;
.
.
.

      srand (time(0));

      printf ("How many random numbers would you like: ");
      scanf ("%d", &i);

      for (j=0; j<i; j++)
      {
              fprintf (filepointer, "%d\n", rand ());
      }

---

call srand only once and you get good random numbers.

next thing, reading in from the user: use fgets to read in strings,
its probably the best function to use. see this

now IMO it would be better to write this program as just 1
function, that way you can avoid using pointers because you
dont seem to be too confident with how they work, and also
this program is not too complex either, although it may seem
challenging at the moment.

file i/o should be ok for you, just read any of the tutorials on
it on this site, like this

id like to help more but i dont want to end up writing the bulk
of the code for you because this is a good learing exercise
for file i/o. i just recommend reading up on the things i highlighted
and making sure that you understand them clearly. If you
run into specific problems with stuff you dont get then come back

Thanks Richie. I totally agree with what you said about the random numbers, fgets, and that fact that I don't need to be using so many functions. The problem is that I'm required to use these functions, and the for loop in main() to generate and print these random numbers to the file the user types. I just don't know how to call those functions correctly.

Am I anywhere close with this:

Code:

---

int main(void)
{
    FILE  *ofp;
    int    i,n=0;
    char  filename;

    get_info(filename, n);
    ofp = cfopen(filename, "r+");

      for(i=1; i<=n; ++i){
          fprintf(ofp, "%12d", rand());
          if(i%6 == 0 || i == n)
              fprintf(ofp, "\n");
    }
}

---

Am I calling get_info correctly? I don't have a PC with a compiler right now so I can't use that. I'm just trying to get close right at the moment. :confused:

i was in the middle of a reply but i've decided to work with your
last post.

the problem is that you're calling you're function get_info
and passing it parameters but the parameters have no values -
not good. also, the parameters in get_info are pointers, they cant
take actual data, only memory addresses. change to:

get_info(&filename, &n);

what is the function gfopen supposed to do?

I am suppose to use these three functions in this program. They give cfopen, and we are to write gfopen. I think I have it correct. Should it not be there or is it incorrect?

well IMO the code for cfopen isn't that hot, but if you have to use
it then i guess you have to. so gfopen is probably supposed
to write to the file you specified. i mean, this line

Code:

---

if(strcmp(mode, "w") == 0 && (fp = fopen(filename, "r")) != NULL){

---

i think that's trying to test to see if the file exits - the problem
is that it will probably create the file if it doesn't exist.

i have to go for about an hour so leave it with me and i'll try
and figure out what it is you need.

just so we are clear - you have to generate a user defined
number of random numbers, and write these to a text file -
nothing else?

yes, sir. to a text file that the user also defines.

This is what I have so far:

Code:

---

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

void get_info(char *filename, int *n_ptr);

FILE *cfopen(char *filename, char *mode);

FILE *gfopen(char *filename, char *mode);

int main(void)
{
    FILE  *ofp;
    int    i,n=0;
    char  filename[120];

    get_info(filename, &n);
    ofp = cfopen(filename, "r+");

      for(i=1; i<=n; ++i){
          fprintf(ofp, "%12d", rand());
          if(i%6 == 0 || i == n)
              fprintf(ofp, "\n");
    }
}

void get_info(char *filename, int *n_ptr)
{
    prinf("\n%s\n\n%s",
        "This progam creates a file of random numbers.",
        "How many random numbers would you like?  ");
    scanf("%d", n_ptr);
    printf("\nIn what file would you like them?  ");
    scanf("%s", filename);
}




FILE *cfopen(char *filename, char *mode)
{
    char  reply[2];
    FILE  *fp;
 
    if(strcmp(mode, "w") == 0
      && (fp = fopen(filename, "r")) != NULL){
        fclose(fp);
        printf("\nFile exists.  Overwrite it? ");
        scanf("%1s", reply);
        if(*reply != 'y' && *reply != 'Y') {
        printf("\nBye!\n\n");
        exit(1);
        }
      fp = gfopen(filename, mode);
      return fp;
}



FILE *gfopen(char *filename, char *mode)
{
    FILE *fp;
   
    if((fp = fopen(filename,mode)) == NULL){
    fprintf(stderr, "Cannot open %s - bye!\n", filename); 
    exit(1);
    }
    return fp;
}

---

> char filename;

> get_info(&filename, &n);

You need a char array to hold the filename, "char filename" is just one char. Also you don't need the address (&) for passing filename, that's the default, so:

Code:

---

    char  filename[120];

    get_info(filename, &n);

---

Code:

---

prinf("\n%S\n\n%s",

---

what's prinf?
%S is not a valid format specifier

you have unbalanced parantheses in function cfopen

You are trying to store a string in filename, but you've only allocated space for a single character.
You need a character array.

If you change filename to an array, you do not need the address operator '&' when passing to functions.

You need to include string.h if you plan to use string functions

Edit: string stuff already mentioned by Swoopy

Use srand() for better random numbers. See Richie T's first post.

Quote:

---

Code:

---

if(strcmp(mode, "w") == 0 && (fp = fopen(filename, "r")) != NULL){

---

i think that's trying to test to see if the file exits - the problem
is that it will probably create the file if it doesn't exist.

---

If you open a file in mode "r", the file isn't created. fopen() returns 0 in that case.

I fixed up the printf statement. The %s was wrong, and the other parentheses is at the end of the second sentence: "How many would you like to see?" I also changed the filename to an array.

Does it work now? Post your code.

Here goes:

Code:

---

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

void get_info(char *filename, int *n_ptr);

FILE *cfopen(char *filename, char *mode);

FILE *gfopen(char *filename, char *mode);

int main(void)
{
    FILE  *ofp;
    int    i,n=0;
    char  filename[120];

    get_info(filename, &n);
    ofp = cfopen(filename, "r+");

      for(i=1; i<=n; ++i){
          fprintf(ofp, "%12d", rand());
          if(i%6 == 0 || i == n)
              fprintf(ofp, "\n");
    }
}

void get_info(char *filename, int *n_ptr)
{
    prinf("\n%s\n\n%s",
        "This progam creates a file of random numbers.",
        "How many random numbers would you like?  ");
    scanf("%d", n_ptr);
    printf("\nIn what file would you like them?  ");
    scanf("%s", filename);
}




FILE *cfopen(char *filename, char *mode)
{
    char  reply[2];
    FILE  *fp;
 
    if(strcmp(mode, "w") == 0
      && (fp = fopen(filename, "r")) != NULL){
        fclose(fp);
        printf("\nFile exists.  Overwrite it? ");
        scanf("%1s", reply);
        if(*reply != 'y' && *reply != 'Y') {
        printf("\nBye!\n\n");
        exit(1);
        }
      fp = gfopen(filename, mode);
      return fp;
}



FILE *gfopen(char *filename, char *mode)
{
    FILE *fp;
   
    if((fp = fopen(filename,mode)) == NULL){
    fprintf(stderr, "Cannot open %s - bye!\n", filename); 
    exit(1);
    }
    return fp;
}

---

Code:

---

scanf("%s", filename);

---

You might want to use fgets().

Code:

---

scanf("%1s", reply);

---

You might want to use fgets() or getchar() here.

And you should close the file:

Code:

---

fclose(ofp);

---

Other than that (and the lack of consts), it's a good program. Congrats.

Sorry, I meant unbalanced brace in function cfopen.
I'm not sure what your trying to do, but this is what it looks like with more consistent indentation

Code:

---

FILE *cfopen(char *filename, char *mode)
{
    char  reply[2];
    FILE  *fp;

    if(strcmp(mode, "w") == 0 && (fp = fopen(filename, "r")) != NULL)
    {  // '{' <--- never closed
        fclose(fp);
        printf("\nFile exists.  Overwrite it? ");
        scanf("%1s", reply);

        if(*reply != 'y' && *reply != 'Y')
        {
            printf("\nBye!\n\n");
            exit(1);
        }

    fp = gfopen(filename, mode);
    return fp;
}

---

You still have a prinf instead of printf in get_info

Thanks to both of you guys. 1. I can understand better how to actally call the function correctly. 2. I can see how the filename is passed around correctly.

Thanks again.

Hey guys. I have visualstudio.net as to write my code on. When I run this code, it doesn't let me enter the file. It just comes up with an error message that says that it can't find the specified file.
It's interactive though. It's suppose to ask me what file to put the random numbers in. Any suggestions?

Code:

---

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

void get_info(char *filename, int *n_ptr);

FILE *cfopen(char *filename, char *mode);

FILE *gfopen(char *filename, char *mode);

int main(void)
{
    FILE  *ofp;
    int    i,n=0;
    char  filename[120];

    get_info(filename, &n);
    ofp = cfopen(filename, "r+");

      for(i=1; i<=n; ++i){
          fprintf(ofp, "%12d", rand());
          if(i%6 == 0 || i == n)
              fprintf(ofp, "\n");
    }
    fclose(ofp);
}

void get_info(char *filename, int *n_ptr)
{
    printf("\n%s\n\n%s",
        "This progam creates a file of random numbers.",
        "How many random numbers would you like?  ");
    scanf("%d", n_ptr);
    printf("\nIn what file would you like them?  ");
    scanf("%s", filename);
}




FILE *cfopen(char *filename, char *mode)
{
    char  reply[2];
    FILE  *fp;
 
    if(strcmp(mode, "w") == 0
      && (fp = fopen(filename, "r")) != NULL){
        fclose(fp);
        printf("\nFile exists.  Overwrite it? ");
        scanf("%1s", reply);
        if(*reply != 'y' && *reply != 'Y') {
        printf("\nBye!\n\n");
        exit(1);
        }
      fp = gfopen(filename, mode);
      return fp;
}



FILE *gfopen(char *filename, char *mode)
{
    FILE *fp;
   
    if((fp = fopen(filename,mode)) == NULL){
    fprintf(stderr, "Cannot open %s - bye!\n", filename); 
    exit(1);
    }
    return fp;
}

---

that code still doesn't compile, missing brace before function
gfopen. the problem is with cfopen, i'm sorry to say that the code
for that function is so restrictive, it's really shoddy work, and i
know that's not your fault, you didn't write it. i would take it up
with whoever did write it, because the only way i can get your
program to work is by calling cfopen with "w" instead, AND that
the destination file exists already. as it stands now, cfopen just
won't cut it.

also if its skipping over the part where it's supposed to read in
a file name (this didn't happen for me but i'm on a different
compiler), you'll need to flush the input buffer.

http://faq.cprogramming.com/cgi-bin/...&id=1043284392

okay, I got it so it will run, but my file will not open no matter what I put in there. Is this because of my cfopen function?
This is the first time I've ever done this so I don't know what to expect. Does it write to the file, and we don't see any of it. How do we know if the program was successful?

ya thats kind of what i was getting at, the code for cfopen is
bad, you need to change

ofp = cfopen(filename, "r+");

to this

ofp = cfopen(filename, "w");

now go to what ever directory you are running the executable
from (wherever you/your compiler has it saved) and create a text
document using notepad called "h.txt". you don't need to put
anything in it, but the file extension is important so yo can view it
using notepad (i'm totally assuming you're on windows).
now run the modified code, and for the file name type h.txt.

what that does for me is writes the random numbers into the file
h.txt. thats the only way that the code as it stands at the
moment i think. try what i have said exactly and get back to me
on it. also to answer what you asked, it won't display the values
written to the file on screen, so open the file and you will
see them there

Yeah, I got it to work that way. Thanks. Hey Richie if you have time to look at this one last thing. It's the same program with some modifications I made so that if you input something like 46i instead of 461, it causes an error. I can get it to tell me there is an error and to write to a file, but I don't think it gives me the right number of random numbers. Can you run it and see what you come up with. Thanks man. Am I printing them out right in my for loop?

Code:

---

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

#define MAXLINE  100

FILE *cfopen(char *filename, char *mode);

FILE *gfopen(char *filename, char *mode);

int main(void)
{
    FILE  *ofp;
    int    i;
    char  filename[120],*pEnd ,line[MAXLINE];
   
       

    printf("\n%S\n\n%s",
        "This progam creates a file of random numbers.",
        "Please enter in the number of random numbers you would like to see as a positive integer.  "),
   
        fgets( line, MAXLINE, stdin);
   
    if((strtol(line, &pEnd, 0)) <= 0 || *pEnd != '\n')
        {
            printf("\nERROR: Please enter positive integer.\n");
        }
   
    printf("\nIn what file would you like them?  ");
    scanf("%s", filename);

    ofp = cfopen(filename, "w");

     
       
        for(i=1; i<=(int)line; ++i){
          fprintf(ofp, "%12d", rand());
          if(i%6 == 0 || i == (int)line)
              fprintf(ofp, "\n");
    }
}





FILE *cfopen(char *filename, char *mode)
{
    char  reply[2];
    FILE  *fp;
 
    if(strcmp(mode, "w") == 0
      && (fp = fopen(filename, "r")) != NULL){
                  fclose(fp);}
        printf("\nFile exists.  Overwrite it? ");
        scanf("%1s", reply);
        if(*reply != 'y' && *reply != 'Y') {
        printf("\nBye!\n\n");
        exit(1);
        }
      fp = gfopen(filename, mode);
      return fp;
}



FILE *gfopen(char *filename, char *mode)
{
    FILE *fp;
   
    if((fp = fopen(filename,mode)) == NULL){
    fprintf(stderr, "Cannot open %s - bye!\n", filename); 
    exit(1);
    }
    return fp;
}

---

Read one of the various FAQs on getting input from a user, and pick a different method.


Quzah.

I totally agree with you quzah, but this is what I have to use. The only thing I have left to figure out is how to print the correct number of random numbers into the file using my for loop and using line prints to many which makes sense to me now.

ok what i have discovered is that your validation doesn't change
the entered value back to an int. you may not know this,
but when you read in a string, the numerical values 0-9 are stored
as their ascii values, which do not run from 0-9. ascii character 0
is the decimal value 48, 1 is 49 and so on. check it out with this:

printf ("%c", 48);

so when you casted the value in your loop, you are casting to this
value, well actually you were dealing with the memory address,
in the lool, line was supposed to be *line.

look up atoi. i have to go now, sorry i couldnt help more at the
moment

Code:

---

int main(void)
{
    FILE  *ofp;
    int  i;
    long  input;
    char  filename[120],*pEnd ,line[MAXLINE];

    printf("\n%S\n\n%s",  // Why is this still a capital S
        "This progam creates a file of random numbers.",
        "Please enter in the number of random numbers you would like to see as a positive integer.  "),

    fgets( line, MAXLINE, stdin);

    //Store result of strtol in a long int, instead of doing additional conversion later
    if((input = strtol(line, &pEnd, 0)) <= 0 || *pEnd != '\n')
    {
        printf("\nERROR: Please enter positive integer.\n");
       //since something bad happened... exit (or loop back to try again)
        exit(1);
    }

    printf("\nIn what file would you like them?  ");
    scanf("%s", filename);

    ofp = cfopen(filename, "w");

    for(i=1; i <= input; ++i)
    {
        fprintf(ofp, "%12d", rand());
        if(i%6 == 0 || i == input)
        {
            fprintf(ofp, "\n");
        }
    }

    //CLOSE THE FILE
    //RETURN 0
}

FILE *cfopen(char *filename, char *mode)
{
    char  reply[2];
    FILE  *fp;

    if(strcmp(mode, "w") == 0 && (fp = fopen(filename, "r")) != NULL)
    {
          fclose(fp);
    }

    //I doubt this is what you want... always assume the file already exists?
    printf("\nFile exists.  Overwrite it? ");

    scanf("%1s", reply);
    if(*reply != 'y' && *reply != 'Y')
    {
        printf("\nBye!\n\n");
        exit(1);
    }

    fp = gfopen(filename, mode);
    return fp;
}

---

Thanks a bunch guys. After looking at it for quite awhile last night, I was able to make it work the same way spydoor has it set up. I was going to post that I had it working, but when I was done, I basically colapsed in my chair. Thanks a lot for the help though. I REALLY appreciate it. :cool: