LValue Required

[Goodluck]

Hello

I have written the following code.
Code:
#include<stdio.h>
#include<conio.h>
void main()
{
int i = 0, a = 5, b = 6;
i = a - - b;
printf("i = %d", i);
}

When I execute this program, I have got an error message "LValue Required".
Can any one explain what does that mean.
Please guide. Thanks.

[v0id]

The minus-operator is read from right to left, and in your code does one of the minus-operations miss a value on the left side. It's on line six, where you're having to minus-operators in a row:

i = a - - b;

Either remove one of the minuses, or put something in between. Here is it with one of them removed:

i = a - b;

That would work.

Another thing is your coding style. You should try staying to the standards, and don't be using non-compiler-independent libraries like conio.h. Your main-function is also wrong. It shall return an integer, and not nothing.

[Goodluck]

Thank you for your guidance.

But I don't understand "Non-compiler independent libraries" like conio.h. Why can't I use it? If I want to use a function like getch() then which library should be included?

Why should main() function return an integer value? What it does when we use void?

Sorry, I am a beginner to C. Please guide.

[v0id]

Originally Posted by Goodluck

But I don't understand "Non-compiler independent libraries" like conio.h. Why can't I use it? If I want to use a function like getch() then which library should be included?

conio.h is not a part of the C programming language. It was originally made for the old MS-DOS compilers, but has been ported to newer platforms through the time, but it's by no mean cross-platform, so if you're developing for multiple platforms, this is not the right library to use.
If you just want it to run on the platform you're currently using, then do it. You just have to keep in mind, that it's not a standard library.

Originally Posted by Goodluck

Why should main() function return an integer value? What it does when we use void?

I was actually wrong on this one. I checked the C standard, and realized that it's actually up to the user (or compiler) how the main()-function shall be implemented in C. It's not like that in C++. In C++ you have to implement it using an integer as a return, and that's why I assumed it was the same in C.
The C standard is not online, so this is the best link I could find regarding C and the main()-function:
FGA: "void main()" is not legal in C++ but is legal in C

Originally Posted by Goodluck

Sorry, I am a beginner to C. Please guide.

Don't apologize, we all start somewhere. It's good that you're asking these questions. Many beginners would just think "okay," and just do it, without actually understanding it.

[Goodluck]

Thank you.