Problem with substring program

hello friends,

I wrote a c program to perform the substring operation on the string str[100]. This program was to take the position index pos and the number of characters len that needs to be printed on the screen. variable length stores the length of the string str[100].

Although I am getting the correct output from this program yet, I get additional characters after my output text. Please help me with this situation.

Here is the program that I have coded:-

#include<stdio.h>//extra ouput
void main()
{
char str[100], subs[100];
int len,length = 0, pos,i = 0,j = 0;
printf(" enter the string\n");
gets(str);
printf(" enter the position\n");
scanf("%d", &pos);
printf(" enter the length\n");
scanf("%d", &len);
for( i = 0; str != '\0'; i++)
length++;
i=0;
if((pos+len-1) > length)
printf("invalid query terminating...\n");
else
{
i = pos;
for(j = 0; j<len; j++)
{
subs[j] = str;
i++;
}
}
printf("\n\n displaying the result\n\n");
i = 0;
puts(subs);
}

this program produces extra characters like ?^ at the end of the output text.