Replace word with another word

Write a program to replace one word with another word in file.

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include"fileinfo.h"
void Word_Replace_With_Another_Word(FILE*,char*,char*);
char* Replace_Word_in_String(char*,char*,char*);
int FinalLength = 0;
int main()
{
	//int WordCount = 0;
	char file[32],wordtofind[100],wordtoreplacewith[100];
	FILE *fp;
	printf("Enter file name = ");
	scanf("%[^\n]",file);
	fp = fopen(file,"r+");
	if(fp == NULL)
	{
		printf("file is not present in this directory\n");
		return 0;
	}
	printf("Word to find = ");
	scanf(" %[^\n]",wordtofind);
	printf("Word to Replace with = ");
	scanf(" %[^\n]",wordtoreplacewith);
	Word_Replace_With_Another_Word(fp,wordtofind,wordtoreplacewith);
	return 0;
}
void Word_Replace_With_Another_Word(FILE* fp,char *s,char *r)
{
	char *p,ch;
	char *q=NULL;
	int CharCount,i=0;
	CharCount = Get_Total_Chars(fp);
	p =  (char*)malloc(CharCount);
	while((ch = fgetc(fp)) != EOF)
	{
		p[i] = ch;
		i++;
	}
	p[i] = '\0';
	q = (char*)malloc(sizeof(char) * FinalLength);
	q = Replace_Word_in_String(p,s,r);
	fclose(fp);
	fp = fopen("result","w");
	fputs(q,fp);
	fclose(fp);
}
char* Replace_Word_in_String(char* s1,char *s2,char *s3)
{
	int l1,l2,l3,i,j,m,t;
	l1 = strlen(s1);
	l2 = strlen(s2);
	l3 = strlen(s3);
	char *org,*q = NULL;
	org = s1;
	m = 0;
	while( q = strstr(s1,s2))
	{
		s1=q+l2;
		m++;
	}
	FinalLength = l1-(l2*m)+(l3*m);
	s1 = org;
	q = (char*)malloc((sizeof(char)) * FinalLength);
	m = 0;
	for(i=0;i<l1;i++)
	{
		if(s1[i] == s2[0])
		{
			for(j=1;j<l2;j++)
			{
				if(s1[i+j] != s2[j])
					break;
			}
			if(j == l2)
			{
				for(t=0;t<l3;t++)
				{
					q[m++] = s3[t];
				}
				s1=s1+l2-1;
			}
			else
			q[m++] = s1[i];
		}
		else
		{
			q[m++] = s1[i];
		}
	}
	q[m] = '\0';
	return q;
}

Note: File name info is present in the current working directory.

cat info
It is just
a random text to
check the code
it is wonderful
let me say it is

Output

./a.out
Enter file name = info
Word to find = is
Word to Replace with = IS

cat Result
It IS just
a random text to
check the code
it IS wonderful
let me say it IS