"Expression must be a modifiable LValue"

我正在尝试创建一个物理模拟，模拟所有spaghettiObjects上的物理并将其显示为文本。目前还没有任何物理模拟，但这些会去//math写的地方

我对这段代码有麻烦。我是一个相当新的程序员，我从java开始，并试图学习c++。错误在第48、49、50行，我试图用不同的方法调用做同样的事情。我无法找出什么是错误的在这里，当我删除= worldobjecttouupdate。变量，则不再抛出错误。

下面是所有的代码

#include <iostream>
#include <string>
using namespace std;
//Created to hold the x, y, velocity and mass of an object.  
//It's called a spaghettiObject cause I was bored.
//A better name would probably be something like "worldObject"
struct spaghettiObject {
public:
    float velocity;
    float positionX;
    float positionY;
    float mass;
};
//All world objects in an array
spaghettiObject myArray[5];
//test zone
spaghettiObject test;
spaghettiObject createTestObject() {
    myArray[1] = test;
    test.mass = 2;
    test.positionX = 2;
    test.positionY = 2;
    test.velocity = 2;
    return test;
}
//Output from the physics simulation to the render function
spaghettiObject output;
//Calculates the position of a spaghettiObject's x using velocity
float nextPositionX(spaghettiObject objectToTransform) {
    float objectToTransformNewX = objectToTransform.positionX;
    //math
    return  objectToTransformNewX;
}
//Calculates the position of a spaghettiObject's x using velocity
float nextPositionY(spaghettiObject objectToTransform) {
    float objectToTransformNewY = objectToTransform.positionY;
    //math
    return objectToTransformNewY;
}
//Calculates the new velocity. for use:after updating x and y of object
float nextVelocity(spaghettiObject objectToUpdate) {
    float objectToUpdateNewV = objectToUpdate.velocity;
    //math
    return objectToUpdateNewV;
}
//Designed to be where all of the update functions are called
void updateWorldObject(spaghettiObject worldObjectToUpdate) {
    nextPositionX(worldObjectToUpdate) = worldObjectToUpdate.positionX;
    nextPositionY(worldObjectToUpdate) = worldObjectToUpdate.positionY;
    nextVelocity(worldObjectToUpdate) = worldObjectToUpdate.velocity;
}
//calculates position of variable defined above, myArray
void nextUpdateOfMyArray() {
    //temp object that is effectively the entire array
    spaghettiObject temp;
    //initilization of temp
    temp.mass = 0;
    temp.positionX = 0;
    temp.positionY = 0;
    temp.velocity = 0;
    //for calling functions for
    //each of the objects
    for (int i = 0; i++; i < (sizeof myArray / sizeof spaghettiObject)) {       
        //assigning the current object in the array to the temp object
        myArray[i] = temp;
        //Calling the update functions
        updateWorldObject(temp);
        //test
        createTestObject() = temp;
        //regular code
        output = temp;
    }
}
//Used to update the physics
void update() {
    nextUpdateOfMyArray();
}
//Used to render a console output
void render() {
    cout << output.mass + output.positionX + output.positionY + output.velocity;
}
int main() {
    update();
    render();
    cin.get();
}