Want a C program to write into a file, read it and store even and odd numbers in a separate file

Question

I tried to make the following code.

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

void main()
{
  FILE *fp1,*fp2,*fp3;
  int n,i,size;
  printf("Enter no.of digits: ");
  scanf("%d",&size);
  fp1=fopen("NUMBER.txt","w");
  printf("Enter the numbers: \n");
  for(i=0;i<size;i++)
  {
    fflush(stdin);
    scanf(" %d",&n);
    fputc(n,fp1);
  }
  fclose(fp1);
  
  fp1=fopen("NUMBER.txt","r");
  fp2=fopen("EVEN.txt","w");
  fp3=fopen("ODD.txt","w");
  while((n=fgetc(fp1))!=EOF)
  {
    if(n%2==0)
    fputc(n,fp2);
    else
    fputc(n,fp3);
  }
  fclose(fp1);
  fclose(fp2);
  fclose(fp3);

  fp1=fopen("NUMBER.txt","r");
  fp2=fopen("EVEN.txt","r");
  fp3=fopen("ODD.txt","r");
  
  printf("The content of number file are: ");
  while((n=fgetc(fp1))!=EOF)
  printf(" %d",n);
  
  printf("\nThe content of even file are: ");
  while((n=fgetc(fp2))!=EOF)
  printf(" %d",n);
  
  printf("\nThe content of odd file are: ");
  while((n=fgetc(fp3))!=EOF)
  printf("  %d",n);

  fclose(fp1);
  fclose(fp2);
  fclose(fp3);
}

The problem I face is that the contents of the files are in hex or binary. I want it to be readable with text editor not a hex editor. The other problem I face is the scanf() doesn't accept 3 digit numbers. The output is given below.

Enter no.of digits: 5 Enter the numbers: 123 34 456 67 789 The content of number file are: 123 34 200 67 21 The content of even file are: 34 200 The content of odd file are: 123 67 21

I tried to write the following code:

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

int main()
{
    FILE *fp1,*fp2,*fp3;
    int size,n,a,b;
    printf("Enter the size: ");
    scanf("%d",&size);
    fp1=fopen("numbers1.txt","w");
    fp2=fopen("even1.txt","w");
    fp3=fopen("odd1.txt","w");
    
    printf("Enter the integers: ");
    
    for(int i=0;i<size;i++)
    {
      scanf("  %d",&n);
      //putc(n,fp1); reads as 12, 234 etc but digits in file is not visible
      fprintf(fp1," %d\n",n);//reads 12, 234 as 12234 but digits in file are visible
      
    }
    
    fclose(fp1);
    fp1=fopen("numbers1.txt","r");
    
    n=getc(fp1);
    
    while(n!=EOF)
    {
        if(n%2==0)
        putc(n,fp2);
        
        else if(n%2==1)
        putc(n,fp3);
        
        n=getc(fp1);
    }

    
    fclose(fp1);
    fclose(fp2);
    fclose(fp3);
    
    
    return 0;
}

In the above code the content in the files are in text, but the odd and even files read char by char. The contents of odd, even and number files are given blow.

odd file: 133577

even file: 2 4 46 6 8

Number file: 123 34 456 67 78

Please help me

Answer 1

It is almost always a bad idea to require the number of data points to be specified before the data is given. Generally, the only reason to do that is to simplify the code so that you don't need to grow data structures. In this case, however, you are writing all the data to a file so you don't even need to do that, since the file provides the storage for you.

To write human readable integers, you need to format the data. The most common way to do that is with printf. There are a lot of ways to do what you're asking, and this is just one idea:

#include <limits.h>                                                                
#include <stdio.h>                                                                 
#include <stdlib.h>                                                                
                                                                                   
struct named_file {                                                                
        const char *name;                                                          
        FILE *fp;                                                                  
};                                                                                 
                                                                                   
void xfopen(struct named_file *f, const char *mode);                               
void xfclose(struct named_file *f);                                                
void display(const struct named_file *f);                                          
                                                                                   
int                                                                                
main(void)                                                                         
{                                                                                  
        struct named_file f[3];                                                    
        int n;                                                                     
                                                                                   
        f[0].name = "NUMBER.txt";                                                  
        f[1].name = "EVEN.txt";                                                    
        f[2].name = "ODD.txt";                                                     
                                                                                   
        xfopen(f, "w");                                                            
        while( scanf("%d", &n) == 1 ){                                             
                fprintf(f[0].fp, "%d\n", n);                                       
        }                                                                          
        xfclose(f);                                                                
                                                                                   
        xfopen(f + 0, "r");                                                        
        xfopen(f + 1, "w");                                                        
        xfopen(f + 2, "w");                                                        
                                                                                   
        while( fscanf(f[0].fp, "%d", &n) == 1 ){                                   
                FILE *out = n % 2 ? f[2].fp : f[1].fp;                             
                fprintf(out, "%d\n", n);                                           
        }                                                                          
        for( int i = 0; i < 3; i += 1 ){                                           
                xfclose(f + i);                                                    
                xfopen(f + i, "r");                                                
                display(f + i);                                                    
                xfclose(f + i);                                                    
        }                                                                          
}                                                                                  
     
void                                                                               
xfopen(struct named_file *f, const char *mode)                                     
{                                                                                  
        f->fp = fopen(f->name, mode);                                              
        if( f->fp == NULL ){                                                       
                perror(f->name);                                                   
                exit(EXIT_FAILURE);                                                
        }                                                                          
}                                                                                  
                                                                                   
void                                                                               
xfclose(struct named_file *f)                                                      
{                                                                                  
        if( fclose(f->fp) ){                                                       
                perror(f->name);                                                   
                exit(EXIT_FAILURE);                                                
        }                                                                          
}                                                                                  
                                                                                   
void                                                                               
display(const struct named_file *f)                                                
{                                                                                  
        int n;                                                                     
        printf("The contents of %s: ", f->name);                                   
        while( fscanf(f->fp, "%d", &n) == 1 ){                                     
                printf(" %d",n);                                                   
        }                                                                          
        putchar('\n');                                                             
}