Getting wrong values when rotating vector around axis

I'm trying to add rotation functions to my class, to rotate around the X, Y, Z - axis, but the output is not exactly what i expected

I made sure that my formulas are correct, they seem to be correct, but i don't know. i took them from this : Rotating a Vector in 3D Space

``````#include <iostream>

using namespace std;

#include <math.h>

// Vector class, to handle all the vector operations for us
// Thanks to : https://stackoverflow.com/questions/14607640/rotating-a-vector-in-3d-space
class cVector
{
public:
float x;
float y;
float z;
// Constructor
cVector();
cVector(float x1, float y1, float z1);

// returns the vector's magnitude
float Magnitude();

// Normalize ( change length to 1, while keeping the same direction)
void Normalize();

// Rotate around the Axis
void RotateX(float angle);
void RotateY(float angle);
void RotateZ(float angle);

// TODO : Add operators for Addition & Substraction

cVector operator+(cVector const& v1) const
{
return cVector(x + v1.x,
y + v1.y,
z + v1.z);
}
void operator+=(cVector const& v1)
{
x += v1.x;
y += v1.y;
z += v1.z;
}
// Substraction
cVector operator-(cVector const& v1) const
{
return cVector(x - v1.x,
y - v1.y,
z - v1.z);
}
void operator-=(cVector const& v1)
{
x -= v1.x;
y -= v1.y;
z -= v1.z;
}

// Multiplication
void operator*=(const float scalar)
{
x *= scalar;
y *= scalar;
z *= scalar;
}
cVector operator*(const float scalar) const
{
return cVector(x * scalar,
y * scalar,
z * scalar);
}

// Division
void operator/=(const float scalar)
{
x /= scalar;
y /= scalar;
z /= scalar;
}
cVector operator/(const float scalar) const
{
return cVector(x / scalar,
y / scalar,
z / scalar);
}
};

// Constructor
cVector::cVector()
{

}

cVector::cVector(float x1, float y1, float z1)
{
x = x1;
y = y1;
z = z1;
}

// returns the vector's magnitude
float cVector::Magnitude()
{
return sqrt((x * x) + (y * y) + (z * z));
}

// Normalize ( change length to 1, while keeping the same direction)
void cVector::Normalize()
{
float flMagnitude = Magnitude();

// We devide the coordinates by the magnitude
x /= flMagnitude;
y /= flMagnitude;
z /= flMagnitude;
}

// Rotate around the Axis
void cVector::RotateX(float angle)
{
y = y * cos(angle) - z * sin(angle);
z = y * sin(angle) + z * cos(angle);
}

void cVector::RotateY(float angle)
{
x = (x * cos(angle)) + (z * sin(angle));
z = (-x * sin(angle)) + (z * cos(angle));
}

void cVector::RotateZ(float angle)
{
x = x * cos(angle) - y * sin(angle);
y = x * sin(angle) + y * cos(angle);
}

void PrintVector(cVector vec)
{
cout << "X : " << vec.x << " Y : " << vec.y << " Z : " << vec.z << endl;
}

// TODO : Add operators for Addition & Substraction
int main()
{
cout << "Hello world!" << endl;

cVector vec(10, 0, 0);

vec.RotateZ(1.57f);

PrintVector(vec);

cin.get();
return 0;
}
``````

I expect the method to keep the same magnitude of the vector, and return ( 0, 10, 0) since i'm rotating by pi/2 , but that's not what i'm getting. apparently if i rotate by pi, i get a good result, but other than that, it doesn't work.