All Substrings of a String

/*
Write a program in C for all substrings of a string
*/

#include<stdio.h>
#include<string.h>
#include<malloc.h>

char* substring(char*, int, int);

main()
{
char string[100], *pointer;
int position = 1, length = 1, temp, string_length;

printf("Enter a string\n");
gets(string);

temp = string_length = strlen(string);

printf("Substring of \"%s\" are\n", string);

while ( position <= string_length )
{
while ( length <= temp )
{
pointer = substring(string, position, length);
printf("%s\n", pointer);
free(pointer);
length++;
}
temp--;
position++;
length = 1;
}

return 0;
}