Thread: Finding differences around a point

Hello Salem,
thanks for looking into my code. I am providing you a better examaple here to help me.
Suppose I have a data file containing only one column of positive integers.
On opening my data file, it looks like the following:
4589
1459
3628
1574
6369
4895
1113
4777
5557
2111

Now if I input 5, a new file with 2 columns should be created and on opening it should look as:
0 (4th value - 6th value) /* i.e. 1574-4895 */
1 (3th value - 7th value) /*i.e. 3628-1113 */
2 (2th value - 8th value)
3 (1st value - 9th value)

write until there is no pairs to find the difference!!

Now if I input 5.5, a new file with 2 columns should be created and on opening it should look as:
0 (5th value-6th value) /*i.e. 6369-4895 */
1 (4th value-7th value) /*i.e. 1574-1113 */
2 (3th value-8th value)
3 (2th value-9th value)
4 (1st value-10th value)

write until there is no pairs to find the difference!!
I will only input positive integer or positive half-integer.
Thanks again for your help.
Raja.

Do you mean something like this:

Code:

#define MAX_SIZE 1000  // or whatever is appropriate
...

    double pivot;
    int low, high;
    int n[MAX_SIZE];
    int size;
    
    // read data file into n
    // and set size to it's size
    ...

    printf("Enter pivot: ");
    scanf("%lf", &pivot);

    if (pivot == (int)pivot) {
        low = (int)pivot - 1;
        high = low + 2;
    }
    else {
        low = (int)pivot;
        high = low + 1;
    }

    // adjust for 0-based indexing
    // (your input seems to be 1-based)
    low--;
    high--;

    int i = 0;
    while (low >= 0 && high < size) {
        printf("%d %d\n", i, n[low] - n[high]);
        low--;
        high++;
        i++;
    }

Hello algorism,
Please append to my previous program!
I am getting error..after your suggestion I now modified the program, see below and correct:

Code:

#include <stdio.h>
#include <stdlib.h>
#define MAX 1024
int main(int argc,char *argv[])
{    FILE *fs,*ft;
    char *foldpoint;
    int i,low,high,n[MAX],size;
    double fp;
    if(argc!=4)
    {puts("Improper number of arguments");
     exit(0);
    }
fs=fopen(argv[1],"r");
if(fs==NULL)
        {
        puts("Cannot open source file");
        exit(0);
        }
ft=fopen(argv[2],"w");
if(ft==NULL)
    {
    puts("Cannot open target file");
    fclose(fs);
    exit(0);
    }
foldpoint=argv[3];
sscanf(foldpoint,"%lf",&fp);
printf("Folding point= %lf\n", fp);
while (fgets(line, sizeof(line), fs))
            {i++;
            if(i == fp )
            {printf("%lf is %s",fp,line);   
            }
            }
if(fp==(int)fp) {
        low = (int)fp-1;
        high = low + 2;
    }
    else {
        low = (int)fp;
        high = low + 1;
    }
 
    low--;
    high--;
size=0;
        while (low >= 0 && high < size) {
        fprintf("%d %d\n", i, n[low] - n[high]);
        low--;
        high++;
        i++;
    }
/* writing to file */     
   for (i=0;i<size;i++)
   {
   fprintf(ft, "%f     %f\n", i,n[low]-n[high]);
   }
 fclose(fs);
 fclose(ft);
}

Can you not read the errors/warnings and fix them yourself?

There are 3 errors/warnings (line numbers refer to your code above) :

Line 29: You are using line without defining it anywhere

Line 48: You are using fprintf without giving the first parameter as a FILE* (presumably ft).

Line 56: You are using %f where you should be using %d. Although this bit of code is not needed and won't work anyway.

Also, on line 46 you are setting size to 0 (!) where you should be setting i to 0.

Your biggest problem at the moment is that you seem to expect the n array to magically fill up with the values in your file. That won't happen. You actually have to read them in yourself. Your fgets loop from 29 to 34 is printing out the fold point but not reading the values into n.

BTW, I won't read your code any more if it's presented in this arbitrary "style". If you expect other people to read your code you need to show them the respect of presenting it in a sane manner.

Maybe something like this:

Code:

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

#define MAX 1024

int main(int argc, char *argv[])
{
  FILE *fs, *ft;
  char *foldpoint, line[MAX];
  int i, low, high, n[MAX], size;
  double fp;
   
  if (argc != 4) {
    puts("Improper number of arguments");
    exit(0);
  }

  fs = fopen(argv[1], "r");
  if (fs == NULL) {
    puts("Cannot open source file");
    exit(0);
  }

  ft = fopen(argv[2], "w");
  if (ft == NULL) {
    puts("Cannot open target file");
    fclose(fs);
    exit(0);
  }
 
  foldpoint = argv[3];
  sscanf(foldpoint, "%lf", &fp);
  printf("Folding point= %lf\n", fp);
 
  i = 0;
  while (fgets(line, sizeof(line), fs)) {
    sscanf(line, "%d", &n[i]);
    i++;
    if (i == (int)fp) {
      printf("%lf is %s", fp, line);
    }
  }
  size = i;

  if (fp == (int)fp) {
    low = (int)fp - 1;
    high = low + 2;
  }
  else {
    low = (int)fp;
    high = low + 1;
  }

  low--;
  high--;

  i = 0;
  while (low >= 0 && high < size) {
    fprintf(ft, "%d  %d\n", i, n[low] - n[high]);
    low--;
    high++;
    i++;
  }

  fclose(fs);
  fclose(ft);
  
  return 0;
}

Hello algorism,
I have written the same code with a small change, just included 'sum', in the second 'while' statement. Actually I wanted to write a file not with differences, but with its addition around the fp. But the sum of the squares of the differences around the fp should be displayed on the screen. The code compiles error free and gives the correct and expected result (I think). I made a small calculation using excel and it seems it is correct. It will be nice if you have a look at it for any errors.

Code:

#include <stdio.h>
#include <stdlib.h>
#define MAX 10000
 
int main(int argc, char *argv[])
{
  FILE *fs, *ft;
  char *foldpoint, line[MAX];
  int i, low, high, n[MAX], size,sum;
  double fp;
    
  if (argc != 4) {
    puts("Improper number of arguments");
    exit(0);
  }

  fs = fopen(argv[1], "r");
  if (fs == NULL) {
    puts("Cannot open source file");
    exit(0);
  }

  ft = fopen(argv[2], "w");
  if (ft == NULL) {
    puts("Cannot open target file");
    fclose(fs);
    exit(0);
  }

  foldpoint = argv[3];
  sscanf(foldpoint, "%lf", &fp);
  printf("Folding point= %lf\n", fp);
  
  i = 0;
  while (fgets(line, sizeof(line), fs)) {
    sscanf(line, "%d", &n[i]);
    i++;
    if (i == (int)fp) {
      printf("%lf is %s", fp, line);
    }
  }

  size = i;
  if (fp == (int)fp) {
    low = (int)fp - 1;
    high = low + 2;
  }
   else {
    low = (int)fp;
    high = low + 1;
   }

  sum=0;
  low--;
  high--;
  i = 0;
  while (low >= 0 && high < size) {
    /* sscanf(line,"%d %d", &i, &n[i] ); */
    fprintf(ft, "%d  %d\n", i, (n[low]+n[high]));
    /* printf("%d  %d\n", i, (n[low]-n[high])*(n[low]-n[high])); */
    sum=sum+((n[low]-n[high])*(n[low]-n[high]));
    low--;
    high++;
    i++;
  }

printf("Sum of least sqaures= %d\n", sum);
  
fclose(fs);
fclose(ft);

return 0;
}

Thanks and regards,
Raja.