Sorting by Last Name

[simulationspecimen]

So I have a text file with students names. I made a struct with first names, last names, and grade. I'm supposed to sort the names by last name. The way I sorted works when the last name is defined as a string, but I need to define it as char lastname[50]. And when I do that, it doesn't sort.

  struct student
{
	char firstname[50];
	char lastname[50];
	int testscore;
	char grade;
};

case 1:
			for (int i = 0; i < 20; i++)
			{
				for (int i = 0; i < 20; i++)
				{
					(s[i].lastname, s[i + 1].lastname);
					if (s[i].lastname > s[i + 1].lastname) 
						swap(s[i], s[i + 1]);
				}
			}
			for (int i = 0; i < 20; i++)
				cout << s[i].firstname << " " << s[i].lastname << endl;

[salem c]

		for (int i = 0; i < 20; i++)
			{
				for (int i = 0; i < 20; i++)

You need different loop variables.
You can't use i for both, and expect it to do what you want.

> if (s[i].lastname > s[i + 1].lastname)
This would be fine, if you'd used std::string as your data type.
But as it stands, you need to use strcmp() instead.

> swap(s[i], s[i + 1]);
Is this std::swap, or some random thing you wrote?
If it's your thing, are you parameters reference (good) or value (bad)?

[keskiverto]

Array decays to pointer in that. Comparing addresses of two memory locations does not tell anything about the content of those locations.

You appear to have C-strings in in your arrays. For them, The C Library has:
http://www.cplusplus.com/reference/cstring/strcmp/

[simulationspecimen]

Yea the swap is this function I predefined:

void swap(student &a, student &b) //Function to swap when comparing to put in order
{
	student temp;
	temp = a;
	a = b;
	b = temp;
}

I predefined it as I used it many times.

I understand that I need to use strcmp(), but I'm not sure how to implement it in my function.

I also changed the loop variables and it outputed the names correctly, but not in the order I wanted:

for (int i = 0; i < 20; i++)
			{

				for (int i = 0; i < 19; i++)
				{
					(s[i].lastname, s[i + 1].lastname));
					if (s[i].lastname > s[i + 1].lastname) 
						swap(s[i], s[i + 1]);
				}
			}
			for (int i = 0; i < 20; i++)
				cout << s[i].firstname << " " << s[i].lastname << " " << s[i].grade << endl;

[salem c]

> I also changed the loop variables and it outputed the names correctly, but not in the order I wanted:
But you didn't fix your nested loop variables!

$ g++ -Wall -Wextra -Wshadow bar.cpp
bar.cpp: In function ‘int main()’:
bar.cpp:28:14: warning: declaration of ‘i’ shadows a previous local [-Wshadow]
     for (int i = 0; i < 20; i++)
              ^
bar.cpp:26:10: note: shadowed declaration is here
 for (int i = 0; i < 20; i++)
          ^

> I understand that I need to use strcmp(), but I'm not sure how to implement it in my function.
Did you read keskiverto's link?
I mean, it has an example and everything.
At least enough for you to make an attempt.