As we know terrain might be rendered from heightmap (some raw data prepared with the aid of photoshop) and from mesh which You for example prepare in some 3D tool like Blender. I am actually using the second way of terrain. I have rendered terrain with the aid of mesh. And I have object located at (x,z) and now I have to calculate height of the object location - coordinate y. So I have to find triangle from my terrain mesh which consists (x,z). I have problem with "if" condition. Could You help me to fulfill all the possibilities of "if" condition?

vector< D3DXVECTOR > terrainVerts;  //each entry has 3 floats (x,y,z) of vertex
vector< vector<u32> > terrainFace;   //each entry has 3 DWORD vertex indices


void Object::updateHeightForObject(D3DXVECTOR3& entry);
{
float x = entry.x; //x coordinate of my object
float y = entry.y; //y coordinate of my object which I need update 
float z = entry.z; //z coordinate of my object

u32 numFaces = static_cast<u32>(terrainFace.size());

for(u32 i=0; i<numFaces; ++i)
{
float x1 = terrainVerts[ terrainFace[i][0] ].x;
float x2 = terrainVerts[ terrainFace[i][1] ].x;
float x3 = terrainVerts[ terrainFace[i][2] ].x;
float y1 = terrainVerts[ terrainFace[i][0] ].y;
float y2 = terrainVerts[ terrainFace[i][1] ].y;
float y3 = terrainVerts[ terrainFace[i][2] ].y;
float z1 = terrainVerts[ terrainFace[i][0] ].z;
float z2 = terrainVerts[ terrainFace[i][1] ].z;
float z3 = terrainVerts[ terrainFace[i][2] ].z;

if(x > x1 && x < x2 ????   //there must be some complex if
{
      //triangle found
      //when I find triangle then I have to use some algorithm which I have in my heightmap class in order to get calculate height offset value
, however this is easy for me, because I have implementation}

}
}