Why Is My Helloworld Function Not Declared in This Scope

Why is my HelloWorld function not declared in this scope?

You need to either declare or define the function before you can use it. Otherwise, it doesn't know that HelloWorld() exists as a function.

Add this before your main function:

void HelloWorld();

Alternatively, you can move the definition of HelloWorld() before your main():

#include <iostream>
using namespace std;

void HelloWorld()
{
  cout << "Hello, World" << endl;
}

int main()
{
  HelloWorld();
  return 0;
}

function was not declared in this scope?

You are supposed to declare all functions before you use them. Simple way to do that is to use a prototype.

// prototype
int find_largest(int values[], int size);

int main(){
    ...
}

int find_largest(int values[], int size) {
    ...
}

Function not declared in scope

This error is from your wrong syntax.

int *insert(int *, const int) is a function that returns 'int *' with name 'insert', not a function that returns 'int' with name '* insert'.

Therefore, you need to include 'insert' to your class's namespace, not '* insert'.

As code,

//inserts element into vector before the element at pPosition, if array is full array size is the increased 
int *UBVector::insert(int *pPosition, const int val){
   if(num_items == current_capacity){
      reserve(2*current_capacity);
   }
   for(size_t i=num_items; i>*pPosition; --i){
      item_ptr[i] = item_ptr[i-1];
   }
   item_ptr[*pPosition] = val;
   ++num_items;
}

//removes element at pPosition from vector, shifts all elements over and empties last element in vector
int *UBVector::erase(int *pPosition){
   if(*pPosition < num_items){
      for(size_t i=*pPosition; i<num_items-1; ++i){
         item_ptr[i] = item_ptr[i+1];
      }
      item_ptr[num_items-1] = int();
      num_items--;
   }
}

In other functions, you use right syntax, so, as I think, it's just a mistake, isn't it?

Function 'not declared in this scope', but it is! Isn't it?

It should be world->initPhysics(), not world<-initPhysics()

Your version is being read as the expression "world is less than -1 multiplied by the result of the global function initPhysics()" and it's that global function that it can't find.

And although this is obviously test code, I'd just like to point out that if you allocate an object with new, you must explicitly delete it somewhere.

Function not declared in scope even after declaring it before int main in C++

x_list and y_list are local variables inside of main(), so they are out of scope of the code in x_i() and y_j(). You would have to pass in the variables as extra parameters to those functions, just like you do with display(), eg:

double x_i(const vector<double> &x_list, int node_number)
{
    return x_list[node_number-1];
}

double y_j(const vector<double> &y_list, int node_number)
{
    return y_list[node_number-1];
}

...

int main(){
    ...
    vector<double> x_list;
    vector<double> y_list;
    double d;
    ...
    d = x_i(x_list, some_node_number);
    ...
    d = y_j(y_list, some_node_number);
    ...
}

was not declared in this scope' error

The scope of a variable is always the block it is inside. For example if you do something like

if(...)
{
     int y = 5; //y is created
} //y leaves scope, since the block ends.
else
{
     int y = 8; //y is created
} //y leaves scope, since the block ends.

cout << y << endl; //Gives error since y is not defined.

The solution is to define y outside of the if blocks

int y; //y is created

if(...)
{
     y = 5;
} 
else
{
     y = 8;
} 

cout << y << endl; //Ok

In your program you have to move the definition of y and c out of the if blocks into the higher scope. Your Function then would look like this:

//Using the Gaussian algorithm
int dayofweek(int date, int month, int year )
{
    int y, c;
    int d=date;

    if (month==1||month==2)
    {
         y=((year-1)%100);
         c=(year-1)/100;
    }
    else
    {
         y=year%100;
         c=year/100;
    }
int m=(month+9)%12+1;
int product=(d+(2.6*m-0.2)+y+y/4+c/4-2*c);
return product%7;
}

Function 'not declared in this scope', but it is! Isn't it?

It should be world->initPhysics(), not world<-initPhysics()

Your version is being read as the expression "world is less than -1 multiplied by the result of the global function initPhysics()" and it's that global function that it can't find.

And although this is obviously test code, I'd just like to point out that if you allocate an object with new, you must explicitly delete it somewhere.

Non-trivial Not declared in this scope errors

double area = stepSize = sum = 0; is only a declaration for area and assumes stepSize and sum are already declared. They are not.
Change it to

double area, stepSize, sum;
area = stepSize = sum = 0;

Also

currrentSubintervals

and

currentSubintervals 

are two different things. To this, I can only say - WTH bro?

accelerometer' and 'lcd' not declared in this scope

accelerometer is declared in initialiseAccel. It will go out of scope at the end of that function, and is not a known name in PIT0_IRQHandler. You should probably create a class to hold those variables and functions, or you'll have to use global variables (possibly in a namespace) to hold those values.

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