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.

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.

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.