Why I have to assign ( initialize ) array passed to function

hello Keil
still I donot understand why I should initialize array passed to function inside that function although it is completed in calling function

ex like this part
if i make line ExprTokens[TOKEN_NUM-1][TOKEN_LEN-1]=0; then every thing ok
and if omitted then program hang in communation part with SD ( sd rx buffer problem)

double ExprEvaluation( char ExprTokens[TOKEN_NUM][TOKEN_LEN],char Tkn)
{ uint8_t i,j,k; double t0,t1,t2,t3; ExprTokens[TOKEN_NUM-1][TOKEN_LEN-1]=0; // if not exist cause browser hang
...

thanks in advance