Reading a list of integers from a file

Dev Shed Forums Sponsor:

November 26th, 2012, 10:41 PM

Astrodude

Registered User

Join Date: Oct 2012

Posts: 22

Time spent in forums: 3 h 57 m 34 sec
Reputation Power: 0

Reading a list of integers from a file

I need to write a program that reads a list of integers from a text file. The list of integers is of arbitrary size(up to 1000) and only one integer is contained on each line. The first integer gives the number of values.

Then, I need to write the largest, smallest, and the average to a text file.

Here is part of it where I test the reading in part. What am I doing wrong as far as reading in goes?

Code:

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
void main(){
	
	FILE *fp;
	char sample_chr;
	fp = fopen("numbers-inp.txt", "r");
	int lines;
	lines=0;
	sample_chr = getc(fp);
	while (sample_chr != EOF) 
	{
	
	if (sample_chr == '\n')
	{
	
	lines+=1;
	}
	
	sample_chr = getc(fp);
	}
	 

	

	int num[1000],i;
	 for(i=0; i<lines; i++){
		 
		 

		 fscanf(fp,"%d",&num[i]);
		 printf("%d",num);
	}
	 
	 
}

November 26th, 2012, 11:42 PM

shilpac

Contributing User

Join Date: Oct 2012

Posts: 30

Time spent in forums: 11 h 3 m 34 sec
Reputation Power: 1

Quote:

Originally Posted by Astrodude

Code:

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
void main(){
	
	FILE *fp;
	char sample_chr;
	fp = fopen("numbers-inp.txt", "r");
	int lines;
	lines=0;
	sample_chr = getc(fp);
	while (sample_chr != EOF) 
	{
	
	if (sample_chr == '\n')
	{
	
	lines+=1;
	}
	
	sample_chr = getc(fp);
	}
	 

	

	int num[1000],i;
	 for(i=0; i<lines; i++){
		 
		 

		 fscanf(fp,"%d",&num[i]);
		 printf("%d",num);
	}
	 
	 
}

By the time fscanf happens fp will be pointing to EOF. So it cant read further so reset fp to 0th position.

Code:

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
void main(){

        FILE *fp;
        char sample_chr;
        fp = fopen("numbers-inp.txt", "r");
        int lines;
        lines=0;
        sample_chr = getc(fp);
        while (sample_chr != EOF)
        {

        if (sample_chr == '\n')
        {

        lines+=1;
        }

        sample_chr = getc(fp);
        }

         fseek(fp,0, SEEK_SET); // Code change


        int num[1000],i;
         for(i=0; i<lines; i++){



                 fscanf(fp,"%d",&num[i]);
                 printf("%d",num[i]);   // Code change
        }


}

November 26th, 2012, 11:48 PM

salem

Contributed User

Join Date: Jun 2005

Posts: 3,839

Folding Points: 153 Folding Title: Novice Folder

Time spent in forums: 2 Months 3 Weeks 2 Days 19 h 1 m 4 sec
Reputation Power: 1774

> void main()
Change this to int main, and put a return 0; at the end of the function.

> fp = fopen("numbers-inp.txt", "r");
> int lines;
A couple of things.
1. You don't check that the file was opened successfully.
2. You can't mix declarations and statements in traditional (C89) C. Did you accept the default of visual studio to create a .cpp (C++) file?

> while (sample_chr != EOF)
Is it necessary to have this loop? Given the format description of your file, I don't think so, unless you specifically have to report the number of lines.

If you DO have to count the lines, then you need to call
rewind(fp);
before scanning the file again.

You can read the file just once by doing something like

Code:

while ( i < 1000 && fscanf(fp,"%d",&num[i]) == 1 ) {
    i++;
}

> printf("%d",num);
This should be
printf("%d",num[i]);

__________________
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper

November 27th, 2012, 02:26 PM

Astrodude

Registered User

Join Date: Oct 2012

Posts: 22

Time spent in forums: 3 h 57 m 34 sec
Reputation Power: 0

So I've changed the code to print out the smallest integer value in a list of integers from a text file.

The value isn't printing still though.

Code:

int main(){
	
	
	FILE *fp;
	
	fp = fopen("numbers-inp.txt", "r");
	int i,small,large;
	int num[1001];
	i=0;
	if(fp!=NULL){
	while ( i < 1000 && fscanf(fp,"%d",&num[i]) == 1 ) 
	{
    i++;
}
	 	 
	int j;		 
	
	small=num[1];
	for(j=2;j=num[0];j++){
		if(small>=num[j]){
			small=num[j];
		}

		
	}
	

	}
	fclose(fp);
	printf("%d",small);
	return 0;
	
}

November 28th, 2012, 12:21 AM

salem

Contributed User

Join Date: Jun 2005

Posts: 3,839

Time spent in forums: 2 Months 3 Weeks 2 Days 19 h 1 m 4 sec
Reputation Power: 1774

> small=num[1];
> for(j=2;j=num[0];j++)
Two things.
1. Arrays start at index 0, not 1
2. j=num[0] should be something else - possibly involving the value of i (the number of elements read previously)

Reading a list of integers from a file

Developer Shed Advertisers and Affiliates