error ‘center’ was not declared in this scope center = white_indexatPoint0x + white_indexatP

This error message is indicating that the variable "center" has not been declared within the current scope, meaning that it has not been defined or initialized before being used. The code is trying to assign a value to "center" using a mathematical expression involving the x-coordinates of two points, but since "center" has not been previously defined, the compiler does not know what it refers to. To fix this error, you need to declare and initialize "center" before using it in this expression.