Keep getting indentifier undefined error in C using any ide - c

Question

So this is my first post. I am preparing for some upcoming college courses on programming, one of them deals with C. I have been teaching myself for a little while and have never encountered this problem before, even though I have used the same code. I am having the issue on any ide that I use, which are MS Visual Studio 2019, and Codeblocks, both 16.01 and 17.12.
The problem is when I try to include an inline function, the compiler brings up an error: identifier "keep_window_open" is undefined, as well as the error: 'keep_window_open':identifier not found.
This never happened until I upgraded Codeblocks from 16.01 to 17.12, so that leads to believe something happened with the compiler or some settings that I don't know about, or how to change.
I have tried going back to Codeblocks 16.01, but still get the same error. All my previous programs, that use the exact same code still compile and run, so I am at a lost and completely frustrated. Enough so to think about changing my major, which I really do not want to do. I enjoy programming. But this problem is killing me.
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
inline void keep_window_open() { char ch; scanf("%s", ch); }
int main()
{
printf ("Lets see if this stupid thing works\n");
keep_Window_open();
return 0;
}
The problem is the line of code:
keep_Window_open();
If I comment it out, the program will compile and run, however I can't see it, because all it does is flash and then close the console window. And I need to use this code to see the output window. As I have said I have used this code in many other programs, most of which are much more complex than this, and they all still compile and run. It is only on new projects that I try to create.
I expect the window to stay open until the user presses and enters a key, like it always has before. I am stuck, and would appreciate some input on how to proceed, other than throw myself in front of a bus.

Answer 1

OK, so I was able to solve the issue in CodeBlocks, but not in Visual Studio. I changed the code to have the inline function below the main function, and now when compiled and run in CodeBlocks (17.12) it works exactly like it should, or how I thought it should.
However when I try the same solution in Visual Studio, after putting the inline function below the main function I now get a new error:
'keep_window_open' redefinition basic types
Since I usually use CodeBlocks for C, Visual Studio for C++ and intellij for java, I am not going to worry about this, as long as it works in CodeBlocks I should be OK. However I am curious as to why it work in one IDE and not the other?
I am new to this programming thing, and there is much to learn, and I know virtually nothing about compilers and linkers, as I am focusing on programming techniques and syntax in several different languages.