C program to extract a substring from the middle of a given string

#include <stdio.h>
#include <conio.h>
int main()
{
char str[100], substr[100];
int i=0, j=0, n, m;
clrscr();
printf("\n Enter the main string : ");
gets(str);
printf("\n Enter the position from which to start the substring: ");
scanf("%d", &m);
printf("\n Enter the length of the substring: ");
scanf("%d", &n);
i=m;
while(str[i] != '\0' && n>0)
{
substr[j] = str[i];
 i++;
j++;
 n––;
}
substr[j] = '\0';
printf("\n The substring is : ");
puts(substr);
getch();
return 0;
}