I'm not sure what your program is trying to do, but let me concentrate on the few obviously incorrect lines.

First, in

int Choice;
scanf ("%s", &Choice);

you have the wrong type for Choice: it is "int" whereas it should be a static array of char (let's say char Choice[32]). In this case you also have to remove the "&" before "Choice" in the scant, so that the code becomes:

char Choice[32];
scanf ("%s", Choice);

Moreover, in

else if(Choice == "Energy") //This isnt working in my compiler.

you are trying to compare two strings with the operator "==". This does not work in C. You should use the function "strcmp" the following way:

#include<string.h>
[...]
else if(strcmp(Choice, "Energy")==0)

You'd even better use the following to prevent any buffer overflow

else if(strncmp(Choice, "Energy", 32)==0)

(replace 32 with the maximum number of elements in Choice)

Edit Note that you should change the first comparison too from

if(Choice == 2817)

to

if(strncmp(Choice, "2817", 32))

because Choice is not an int anymore...

The C compiler doesn't care about formatting, in theory you can do whatever you like, and there's no consensus for what is/isn't "proper formatting".

However, most programmers stick to a specific style so that it's easier to read the source code; and if you're working in a team then it's nice if all programmers on the team use the same style so that all of the source code is consistent. To achieve that, there may be a formal "style guide", and if there is you should follow it.

Beyond that, there are some common rules that almost everyone follows:

• nested blocks that are delimited by braces are indented somehow (with either "N space characters" or "N tab characters") relative to the parent block

• cases of a switch statements will be exceptions to the indentation rules. Typically each case's statements are indented even though there's no braces; and the case keyword itself may or may not be indented by the parent switch's braces.

• either all braces are always on a line by themselves; or starting braces are at the end of the line and ending braces may be at the start of a line containing a related statement

• when a block consists of a single statement; either it always uses braces and is takes up a line by itself, or it never uses braces and shares the same line as its parent.

• the else if pair is always an exception to the "block consists of a single statement" rule (the if is a single statement that is never treated as a separate block, and people pretend else if is a single elseif keyword).

What this means is that (depending on who got their way when arguing about it) this might acceptable:

int main() {
    int area;

    printf("Enter radius: ");
    scanf("%d", &radius);

    switch(radius) {
    case 0:
        return 0;
    case 1:
        return 1;
    }

    if (&radius > -1) {
        area = (int)(3.14159 * radius * radius);
        printf("Area = %d\n", area);
    } else return -1;
    return area;
}

..and this might also be acceptable:

int main()
{
    int area;

    printf("Enter radius: ");
    scanf("%d", &radius);

    switch(radius)
    {
        case 0:
            return 0;
        case 1:
            return 1;
    }

    if (&radius > -1)
    {
        area = (int)(3.14159 * radius * radius);
        printf("Area = %d\n", area);
    }
    else
    {
        return -1;
    }
    return area;
}