How to obtain substring from full string? Please Look.

There are many limitations placed for this code. I am still learning so I need hints for this assignment.

No extra variables, no macros or functions other than GetSubstring can be called.
Main function cannot be changed.

This is my code. Focus on the GetSubstring function part.

#include <stdio.h>
#include <stdlib.h>
char *GetSubstring(const char source[], int start, int count, char result[]);

int main(void)
{
const char source[] = "one two three";
char result[] = "123456789012345678";

puts(GetSubstring("This is really fun", 2, 800, result));
puts(GetSubstring("This is really fun", 261, 9, result));
puts(GetSubstring("This is really fun", 0, 12, result));
puts(GetSubstring(source, 5, 87, result));
puts(GetSubstring(source, 18, 7, result));
puts(GetSubstring(source, 6, 5, result));
puts(GetSubstring(source, 0, 3, result));

return(EXIT_SUCCESS);
}


char *GetSubstring(const char source[], int start, int count, char result[])
{
char *copy = result;
for (; *source != '\0' || *source == source[start]; start--)
{
while (*source != '\0')
{
*result++ = *source++;
}

}

*result += '\0';
return (copy);
}


Current Output is:

This is really fun
This is really fun
This is really fun
one two threey fun
one two threey fun
one two threey fun
one two threey fun

Process returned 0 (0x0) execution time : 0.082 s
Press any key to continue.

Can't do this with C strings.

result is already to pointing to where you need to put the null terminator, so just use =.

Thanks for that I'm trying everything I can to change things around

1. GetSubstring doesn't use the count parameter. Use it, or remove it.

2. Massive out of range values
puts(GetSubstring("This is really fun", 2, 800, result));
puts(GetSubstring("This is really fun", 261, 9, result));
If you use these to index your short strings, then you have undefined behaviour in your code.

3. When you post code, make sure you put [code][/code] tags around the code. It should look like this.