game scoring

I am working on game scoring for a breakout game. I am able to write 100 to the screen but then I want to erase the old score and put 200 on the screen and so on. here is the code I am using.

void drawBitmapText(char *string,float x,float y,float z) 
{  
char *c;
glRasterPos3f(x, y,z);
for (c=string; *c != '\0'; c++) 
{
glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *c);
}
}

void brick_collision()
{
	GLint n=0;
	if(bricks[2][4]==true)
	{
	n+=100;
	str=itoa(n,buffer,10);
	glRasterPos3f(4.0f,2.0f,0.0f);
	glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, '\0');
	drawBitmapText(str,4.0f,2.0f,0.0f);	
	}

	if(bricks[2][3]==true)
	{
	n+=100;
	str=itoa(n,buffer,10);
	glRasterPos3f(4.0f,2.0f,0.0f);
	glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24,'\0');
	drawBitmapText(str,4.0f,2.0f,0.0f);	
	}

	if(bricks[2][2]==true)
	{
	n+=100;
	str=itoa(n,buffer,10);
	glRasterPos3f(4.0f,2.0f,0.0f);
	glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, '\0');
	drawBitmapText(str,4.0f,2.0f,0.0f);	
	}

	if(bricks[2][1]==true)
	{
	n+=100;
	str=itoa(n,buffer,10);
	glRasterPos3f(4.0f,2.0f,0.0f);
	glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, '\0');
	drawBitmapText(str,4.0f,2.0f,0.0f);	
	}

	if(bricks[2][0]==true)
	{
	n+=100;
	str=itoa(n,buffer,10);
	glRasterPos3f(4.0f,2.0f,0.0f);
	glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, '\0');
	drawBitmapText(str,4.0f,2.0f,0.0f);	
	}

I am almost done with my game I just need a little help. let me know if you need more code.