I'm making a checkers game and i don't know whats wrong with it.

So I am making a checkers game and I am still pretty new to c so can you tell me whats wrong with this player move function.
If it would help i can paste the hole thing if you want.

Code:

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int PLAYER_MOVE()
{
  int oldnum,newnum,k,l;
  char old,new;
  printf( "Enter current and next location your checker>>" );
  scanf( " %d%c%d%c", &oldnum, &old, &newnum, &new );
  switch ( old ) {
  case 'a':
    k=0;
  case 'b':
    k=0;
  case 'c':
    k=1;
  case 'd':
    k=1;
  case 'e':
    k=2;
  case 'f':
    k=2;
  case 'g':
    k=3;
  case 'h':
    k=3;
  }
  switch ( new ) {
  case 'a':
    l=0;
  case 'b':
    l=0;
  case 'c':
    l=1;
  case 'd':
    l=1;
  case 'e':
    l=2;
  case 'f':
    l=2;
  case 'g':
    l=3;
  case 'h':
    l=3;
  }
  int t;
  while( t == 0 ) {
  if ( BOARD[oldnum][k].PLAYER_THAT_OWNS == '1' ) {
    if ( ( oldnum - newnum == 1 ) || ( ( BOARD[oldnum][k].RANK == 'k' ) && ( ( oldnum - newnum == 1 ) || ( newnum - oldnum == 1 ) ) ) ) {
    char theoldrankonplayer;
    theoldrankonplayer == BOARD[oldnum][k].RANK;
    BOARD[newnum][l].RANK == theoldrankonplayer;
    BOARD[newnum][l].PLAYER_THAT_OWNS == '1';
    BOARD[oldnum][k].RANK == ' ';
    BOARD[oldnum][k].PLAYER_THAT_OWNS == ' ';
    t++;
    }
  }
  else {
    printf( "Bad move!" );
  }
  }
}

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You're using t before it has been assigned a value:

Code:

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  int t;
  while( t == 0 ) {

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Isn't the whole while loop being skipped frequently?

Don't create massive duplicated switch statements. First off, if it really needed to be a large switch statement then you'd put it inside a function and simply call it twice, not duplicate it.

Secondly, the following is exactly equivalent to the first switch statement:

Code:

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if (old >= 'a' && old <= 'h')
    k = (old - 'a') / 2;

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Also consider initialising all of your variables. Whilst this is not always necessary, it looks like you would benefit from it a lot. Consider what happens if I type in 'z'.