Why am I getting a segmentation fault (pset2 substitution)?

Question

I've written something similar to this code for my answer to pset2 Substitution. The idea is to keep string s the same, but have a variable s_capital that converts s into uppercase. I can't work out why it's returning a segmentation fault after hours of searching around. Some help would be very appreciated :)

#include <stdio.h>
#include <cs50.h>
#include <string.h>
#include <ctype.h>

int main(void)
{
    string s = "hello";
    string s_capital = s;
    for (int i = 0; i < strlen(s); i++)
    {
        s_capital[i] = toupper(s[i]);
    }
    printf("%s", s_capital);
}

Answer 1

string s = "hello"; declares a string literal. By definition, it is immutable. If you try to change a char in that string, you will segfault.

Have a look at my post about string literals for more info.

Also, you'll learn more about this in Week 4, but your line string s_capital = s; does not make a copy of the string called s. It simply creates a new variable that "points" to the same part of memory. That is why you cannot change s_capital either.