A little bug about collision in my program - c++

Question

I'm trying to figure out my problem for an hour.
I'm going to draw what is happening.
char trap = 'Q';
char character = 'L';
....
.Q..
..L.
....
when L moves up and Q moves to right they collide and the program ends. but:
....
.QL.
....
....
when L moves to left and Q moves to right they dont collide the same way as the example above instead, whats happening is:
....
..Q.
....
....
here's my code. sorry for my bad english :(
test if the move is 'w' , 'a' , 's' or 'd' :
void cave::move(int& x, int& y, char m, char unit)
{
if ( m == 'W' || m == 'w' ) // if moves up
{
floor[x][y] = tile;
x -= 1;
for ( unsigned short int x = 0; x < 3; x++ )
{
if ( floor[x][y] == wall && floor[x][y] == trap[x] )
{
x += 1;
trapsMove();
}
}
floor[x][y] = unit;
}
else if ( m == 'A' || m == 'a' ) // if moves to left
{
floor[x][y] = tile;
y -= 1;
for ( unsigned short int x = 0; x < 3; x++ )
{
if ( floor[x][y] == wall && floor[x][y] == trap [x] )
{
y += 1;
trapsMove();
}
}
floor[x][y] = unit;
}
else if ( m == 'S' || m == 's' ) // if moves down
{
floor[x][y] = tile;
x += 1;
for ( unsigned short int x = 0; x < 3; x++ )
{
if ( floor[x][y] == wall && floor[x][y] == trap[x] )
{
x -= 1;
trapsMove();
}
}
floor[x][y] = unit;
}
else if ( m == 'D' || m == 'd' ) // if moves to right
{
floor[x][y] = tile;
y += 1;
for ( unsigned short int x = 0; x < 3; x++ )
{
if ( floor[x][y] == wall && floor[x][y] == trapx] )
{
y -= 1;
trapsMove();
}
}
floor[x][y] = unit;
}
else
control();
return;
}
ai moves function
void cave::trapsMove()
{
int r[3]; // each index will hold the movement of traps
for ( unsigned short int x = 0; x < 3; x++ )
{
r[x] = rand() % 4 + 1;
if ( r[x] == 1 ) // moves up
move(traps_positionX[x],traps_positionY[x],'w',trap[x]);
else if ( r[x] == 2 ) // moves to left
move(traps_positionX[x],traps_positionY[x],'a',trap[x]);
else if ( r[x] == 3 ) // moves down
move(traps_positionX[x],traps_positionY[x],'s',trap[x]);
else if ( r[x] == 4 ) // moves to right
move(traps_positionX[x],traps_positionY[x],'d',trap[x]);
}
return;
}
check if collide
bool cave::collision()
{
for ( unsigned short int x = 0; x < 3; x++ )
{
if ( floor[character_positionX][character_positionY] == trap[x] )
return true;
}
return false;
}

Answer 1

Well it seems from your code that the Trap and Player switch their position.
However the position switch from your Trap (Q) overwrites the Player (L) with a floor tile.
Essentially this happens:
(1) .QL.
(2) .L.. // L and Q inhabit the same tile
(3) ..Q. // Q overwrites L with a '.' tile
Your code suffers from convolution, because you try to either do too much in one function or do it in several different places. This leads to you missing for instance the necessary collision check in the above example.
A better strategy would be to try to structure your program flow. For instance you currently have:
(1) Prompt for a direction
(2) Move player tile
(2a) If player hits a tile which is a Trap or a Wall (typo in your code, must be || instead of &&) move the traps
<-- (2a) is another pitfall where traps can do two moves in a row.
(3) Move the traps
(4) check for collision
(5) repeat from (1)
I think what you wanted was:
(1) Prompt for a direction
(2) Move player tile
(2a) check for collision
(3) Move traps
(3a) check for collision
(6) repeat from (1)
As for the refactoring try to recycle your code. For instance in your move() function the char 'w' (...) only influences the 'x' or 'y' variable. Thus you could write it also as
move(...) {
if((m=='w')||(m=='W')) { y = y+1 }
else if((m=='a')||(m=='A')) { x = x-1 } // same for SD
if(floor[x][y] != wall) {
// set new position to object, if it can't move, just don't set it
}
}
This way you don't have to copy&paste your for-loop with minimal alterations.