Thread: copying a string

substr is an array, not a pointer.
You need to write substr[k] to progress through the array.

Also, read the FAQ on not using gets(), and also pay attention to indentation.

Code:

#include <stdio.h>

#define MAX 81

void substring(char *n, int i, int j)
{
  int k;
  char substr[MAX];
  for (k = 0; k <= j; k++) {
    printf("%c", *(n + i + k));
    *substr = *(n + k + i);
    substr++;
  }
  *substr = '\0';
  printf("%s", substr);
}

int main(void)
{
  char name[MAX];               /* allot space                  */

  printf("Hi, what's your name?\n");
  gets(name);                   /* place string into name array */
  printf("Nice name, %s.\n", name);
  substring(name, 2, 1);

  return 0;
}

Finally, use meaningful names in your function declaration, like
void substring(char *name, int startpos, int length)