Prog#137: copy 'n' character from mth position

C Programming
#1 
/*
copy 'n' character from mth position 
Program#137
*/
#include<stdio.h>
main()
{
int i,n,m,j;
char a[50], b[50];
for(i=0,a[i]=getchar(); a[i]!='$';a[++i]=getchar());
a[i]='\0';
scanf("%d",&n);
scanf("%d",&m);
j=0;
for(i=m;a[i]!='\0'&&j<n;i++)
{
b[i]=a[i];
j++;
}
b[i]='\0';
puts (b);
}