Problem with translations and timers?

I've started OpenGL animation and I am trying to create a program that moves a dot up and down. It's meant to work by if functions, keeping track of when my variable for transformations (y axis) goes above or below 0.9 and -0.9 respectively.

However, on running the applications I briefly see the dot just fly out the top of the window and I can't work out what's going wrong with it. Could anybody take a look and see if they know the problem? Thank you so much - here's the code:

Code:

#include <glut.h>

void display(void);
void timer(void);

float amount = 0.91;

int main(int argc , char **argv)
{
    glutInit(&argc , argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowSize(600 , 300);
    glutInitWindowPosition(250 , 250);
    glutCreateWindow("moving dot");
    glutDisplayFunc(display);
    glutTimerFunc(500 , timer , 0);

    glClearColor(0.0 , 0.0 , 0.0 , 1.0);
    glColor3f(1.0 , 1.0 , 1.0);

    glutMainLoop();
}

void timer(void)
{
    if(amount > 0.9)
    {
        amount = amount - 0.01;
    }

    else if(amount < -0.9)
    {
        amount = amount + 0.01;
    }


    glTranslatef(0.0 , amount , 0.0);
    glutPostRedisplay();
}

void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT);
    glPointSize(5);
    glBegin(GL_POINTS);
    glVertex2f(0.0 , 0.0);
    glEnd();

    glutSwapBuffers();

    glFlush();
    glutTimerFunc(500 , timer , 0);
}

If amount is, say, 0.9 it will never move (it is neither above 0.9, nor below -0.9), so every glTranslate will move the dot by 0.9 in the y direction, forever and ever.