Cannot compile (Not declared & Expected Primary Expression) - c++

Question

So bellow follows a function that will then be called for a main program. My problem is, if I do not declare challInfo as a struct, upon compiling, it will return:
ERROR on page PhotoPoints at line 5, col 21: ‘challInfo’ was not declared in this scope
Meanwhile, if I do declare it (as it is bellow) it returns:
ERROR on page PhotoPoints at line 5, col 30: expected primary-expression before ‘.’ token ERROR on page PhotoPoints at line 7, col 52: expected primary-expression before ‘.’ token ERROR on page PhotoPoints at line 8, col 28: expected primary-expression before ‘.’ token ERROR on page PhotoPoints at line 8, col 60: expected primary-expression before ‘.’ token ERROR on page PhotoPoints at line 8, col 109: expected primary-expression before ‘.’ token ERROR on page PhotoPoints at line 9, col 31: expected primary-expression before ‘.’ token ERROR on page PhotoPoints at line 9, col 66: expected primary-expression before ‘.’ token ERROR on page PhotoPoints at line 9, col 118: expected primary-expression before ‘.’ token ERROR on page PhotoPoints at line 14, col 35: expected primary-expression before ‘.’ token ERROR on page PhotoPoints at line 14, col 57: expected primary-expression before ‘.’ token
I have been looking around the internet, including Stack Overflow, and it always seems the answer to this is specific to each case. I admit I'm lost. Can you help?
float PhotoPoints() {
struct challInfo;
bool isFacingOther();
bool sphereInDark();
bool isCameraOn = challInfo.camera.cameraOn;
bool isFacingOtherResult = isFacingOther();
bool isOppNotInDarkZone = !sphereInDark(challInfo.other.zrState);
bool myMirror = challInfo.me.mirrorTime != 0 && challInfo.me.mirrorTime + ITEM_MIRROR_DURATION > challInfo.currentTime;
bool otherMirror = challInfo.other.mirrorTime != 0 && challInfo.other.mirrorTime + ITEM_MIRROR_DURATION > challInfo.currentTime;
float picturePointValue = 0;
if (isCameraOn && isFacingOtherResult && isOppNotInDarkZone && !myMirror)
{
float bet[3], distance;
mathVecSubtract(bet, challInfo.me.zrState, challInfo.other.zrState, 3);
distance = mathVecMagnitude(bet, 3);
if (distance < PHOTO_MIN_DISTANCE) {
DEBUG(("Not a good shot: too close to the other satellite | "));
return 0.0;
}
picturePointValue = 2.0 + 0.1/(distance - PHOTO_MIN_DISTANCE + 0.1);
if(otherMirror){
picturePointValue = 0;
DEBUG(("Not a good shot: Opposing mirror active |"));
}
}
else if(!isCameraOn){
DEBUG(("Not a good shot: camera off |"));
}
else if(myMirror){
DEBUG(("Not a good shot: my mirror's in the way |"));
}
else if(!isFacingOtherResult) {
DEBUG(("Not a good shot: not facing the other satellite | "));
}
else if(!isOppNotInDarkZone){
DEBUG(("Not a good shot: opponent in dark zone |"));
}
return picturePointValue;
}

Answer 1

You have an error here for every time you have referenced a member of challInfo. You need to include a full declaration so that the compiler can tell what is inside of the struct, nut simply that it is a struct. You have only provided a forward declaration.

Answer 2

struct challInfo;
Should have a definition like:
// Define your camera object
struct Camera {
bool isCameraOn;
}
// Define the object type of challInfo
struct PhotographyInfo {
Camera camera
}
then you can use the object:
PhotographyInfo challInfo{};
challInfo.camera = Camera{true};

Answer 3

you define a struct challInfo then after assign the bool isCameraOn to a data member of that struct. Here is the problem I think you are a bit confused about structs. A struct is in many ways like a class. Where for example I could put something like this in a header file with other class definitions.
struct Example_struct{
int data_mem_a;
bool data_mem_b;
}
Then perhaps use this struct in a class prototype
class example_class{
private:
example_struct struct_instance;
public:
bool get_a_from_struct(){return struct_instance.data_mem_a;};
In your case you would want to make sure that the challInfo struct is defined somewhere, and then declare an instance of it.
challInfo CI;
bool isCameraOn = CI.camera.caneraOn;