Errors with program to replace string with another

Alright I wrote the program the way I thought it should work but I am getting some errors when using subStrBeg, subStrEnd and i together. I understand that they're different data types...but I don't know how exactly to resolve this problem.
I get these errors:

Code:

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r.c:33: warning: comparison between pointer and integer
r.c:35: warning: passing argument 1 of ‘fputs’ makes pointer from integer without a cast
r.c:41: warning: assignment makes integer from pointer without a cast
r.c:43: warning: passing argument 1 of ‘fputs’ makes pointer from integer without a cast

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Code:

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

#define MAX 512
#define _GNU_SOURCE

int main(int argc, char *argv[])
{
  int i = 0;
  FILE *file, *file2;
  char line[MAX], *subStrBeg, *subStrEnd;
  int subStrLen, strLength;

  if (argc != 4)
  {
    printf("You must enter: ./replace old-string new-string file-name\n");
    exit(1);
  }

  file = fopen(argv[3], "r");
  file2 = fopen("temp", "w");

  while (fgets(line,sizeof(line),file) != NULL)
  {
    /* Find when string begins, length of string before
      substring, and then the end of the substring */
    subStrBeg = strstr(line, argv[1]);
    subStrLen = subStrBeg-line;
    subStrEnd = subStrBeg+strlen(argv[1]);
    strLength = strlen(line);

    /* Write left part of string to file */
    for (i=0; i < subStrBeg; i++)
    {
      fputs(line[i], file2);
    }
    /* Write replaced string to file */
    fputs(argv[2], file2);
    /*Write right part of string to file */
    for (i=subStrEnd; i < strLength; i++)
    {
      fputs(line[i], file2);
    }
  }
  /* Close everything */
  fclose (file);
  fclose (file2);
  return 0;
}

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If anyone can show me an example of how to fix this or a internet page that explains what to do in this situation...it would be great :)

Thanks,
Dan

You are comparing a pointer to an integer:

Code:

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  for (i=0; i < subStrBeg; i++)
    {
      fputs(line[i], file2);
    }

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And you are doing the same in other places.

I know I'm doing that. The problem is I don't know a way around doing that. I'm not sure how to convert it to something else...if that's the way I should do it.

Dan

Code:

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for (i=0; i < subStrBeg; i++)

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->

Code:

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for (i=0; i < subStrBeg - line; i++)

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Subtracting the start of the string from a pointer to an index will result in the index itself (a variable of type ptrdiff_t).