C program to replace a pattern with another pattern in the text

#include <stdio.h>
#include <conio.h>
main()
{
char str[200], pat[20], new_str[200], rep_pat[100];
int i=0, j=0, k, n=0, copy_loop=0, rep_index=0;
clrscr();
printf("\n Enter the string : ");
gets(str);
printf("\n Enter the pattern to be replaced: ");
gets(pat);
printf("\n Enter the replacing pattern: ");
gets(rep_pat);
while(str[i]!='\0')
{
j=0,k=i;
while(str[k]==pat[j] && pat[j]!='\0')
{
 k++;
j++;
}
if(pat[j]=='\0')
 {
copy_loop=k;
while(rep_pat[rep_index] !='\0')
 {
new_str[n] = rep_pat[rep_index];
rep_index++;
 n++;
}
}
new_str[n] = str[copy_loop];
 i++;
copy_loop++;
 n++;
}
new_str[n]='\0';
printf("\n The new string is : ");
puts(new_str);
getch();
return 0;
}