File handling and replacing string

[aldrin_ison1]

Hi! I'm new to C and I'm having some problems in my program. It opens a .txt file then copies this to another .txt file but replaces a certain word with another word. It uses command line arguments. Example:

//inside text.txt

love is patient
love is kind
...

./change love MONEY text.txt text_new.txt

Output:
//generates a .txt file <text_new.txt>. inside is

MONEY is patient
MONEY is kind
...

I'm having problems replacing the words. We're asked to use strtok(). Here is my code

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

int main(int argc, char *argv[])
{
        FILE *oldfile;
        FILE *newfile;
        unsigned int i=0;
        char c;
        char str[1000]; //just a random number of elements
        char *result=NULL;

//CHECK NUMBER OF ARGUMENTS
        if (argc<5){
                printf("Error: Not enough input parameters\nUsage: ./exer09_02 <oldword> <newword> <infile> <newfile>\n");
                return 1;
        }
//OPEN FILE
        oldfile = fopen(argv[3],"r");
//CHECK IF FOPEN IS SUCCESSFUL
        if (oldfile==NULL){
                printf("ERROR: %s does not exist\n",argv[3]);
                return 1;
        }
//CREATE NEW FILE
        newfile = fopen(argv[4], "w+");

        if (newfile!=NULL)
                printf("New file <%s> generated!\n",argv[4]);
//COPY CONTENTS OF OLDFILE TO A STRING FOR PARSING       
        c = fgetc(oldfile);
        while(c!=EOF){
                str[i] = c;
                i++;
                c = fgetc(oldfile);
        }
	str[i] = '\0';

//FIND AND REPLACE A WORD WITH ANOTHER WORD
        result = strtok(str," ");
        while(result!=NULL){

                if (strncmp(result,argv[1],strlen(argv[1])-1)==0){
                        strncpy(result,argv[2],strlen(argv[2]));
			fprintf(newfile,"%s ",result);				
		}

		result = strtok(NULL," ");
	}

        fclose(oldfile);
        fclose(newfile);

        return 0;
}

Instead of having a correct result, what happens in my code is it generates a text_new.txt file containing:

MONEYis patient
love is kind
...

Only "love" in the first line gets replaced, and if there are letters exceeding four, it eats away at the characters after. I can't seem to find where I got it wrong. Hope someone helps me. Thanks in advance!

[histrungalot]

Two things:
1. Take a look at what strtok is returning

./a.out love MONEY text.txt t.new.txt
New file <t.new.txt> generated!
[love]
[is]
[B][patient
love][/B]
[is]
[kind
]

The first "love" matches because it matches. The second one doesn't match because it is "patient\nlove".

2. You can't copy the newwork in to where the oldword was because what if the new word, as in this case is larger. You need to do

if (strncmp(result,argv[1],strlen(argv[1]))==0){
	    //strncpy(result,argv[2],strlen(argv[2]));
	    fprintf(newfile,"%s ",argv[2]);				
	  }
          else {
            fprintf(newfile,"%s ",result);
          }