expression evaluation and conversion algorithm

Postfix expression Evaluation algorithm

stack operands;  //the arithmetic stack while (not to the end of expression) {    scanf ("an Op object op");     if (op is  operand)         operands.push (OP);     else if (op is  operator)     {         operand_right = operands.pop ();         Operand_left = operands.pop ();        result =  Operand_left op operand_right;        operands.push (result);     }    else    {         printf ("suffix expression is invalid !");     }}if (Operands.size ()  == 1)     return operands.top () ; else    printf ("suffix expression&Nbsp;is invalid! "); 

Evaluation algorithm of prefix expression

Algorithm one: Start processing from the end of the expression (right-to-left)

Pseudo Code Description:

stack operands;   //operand stack while (not reaching the first expression) {    scanf ("an operand op");     if (Op is operand)         operands.push (OP) ;     else if (Op is operator)     {         operand_left = operands.pop ();         operand_right = operands.pop ();         result  = operand_left op operand_right;         Operands.push (Result);    }    else    {         printf ("prefix expression is invalid!");     }}if (Operands.size ()  == 1) {    return operands.top ( );} else    printf ("prefix  expression is invalid! "); 

Algorithm two: Start processing from the expression header (left to right)

The stack operations;  //operand stack, which can be either a cloud algorithm or an operand while (not to the end of an expression) {    scanf (" An Op object op ");     if (Op is operator)     {         operations.push (OP);    }    else  if (Op is operand)     {        if ( Operations.top ()  is operator)         {             operations.push (OP);         }        else         {            while (Operations.top ()  is  operand)             {                 operand_right = op;                 operand_left = operations.pop ();                 operator =  Operations.pop ();                 op = operand_left operator operand_right;             }             Operations.push (OP);        }    }     else    {        printf ("Prefix  Expression is invalid! ");     }}if (Operations.size ()  == 1)     return operations.tOP (); else    printf ("prefix expression is invalid!"); 

infix expression converted to postfix expression algorithm

stack operators;   //operator Stack while (not to end of expression) {    scanf ("an operand op");     if (Op is operand)     {         printf (OP);     }    else if (Op is Operator)     {        if (op  priority greater than  operator.top ()  && op is not  closing brackets)              operator.push (OP);         else if (Op is   Closing brackets)         {             do            {                 tmp =  Operators.pop ();    &nbsP;            if (tmp is not  corresponds to opening parenthesis)                 {                      printf (TMP);                 }                 else                 {                     break;                 }                 if (Operators.empty ())                 {                     printf ("Infix  Expression is invalid! ");                 }             }while (1);         }        else         {            do             {                 tmp = operators.pop ();                 PRINTF (TMP);        & nbSp;    }while (op  priority is less than  operators.top ());             operators.push (OP);        }     }    else    {         printf ("infix expression is invalid!");     }}while (!operators.empty ()) {    tmp = operators.pop ();     PRINTF (TMP);}

infix expression conversion to prefix expression algorithm

Start processing from the end of an expression

The stack operators;  //operator stack stack operations;  //an operand stack, which can be either an operator or an operand while  ( Not to expression first) {    scanf ("an operand op");    if  (Op is operand)     {        operations.push (OP);     }    else if  (Op is operator)     {         if  (op  priority is greater than  operators.top ()  &&  op is not  opening brackets)              Operators.push (OP);        else if  (op is  left parenthesis)         {             do            {          &nBsp;      tmp = operators.pop ();                 if  (tmp is not  corresponds to closing parenthesis)                  {                      Operations.push (TMP);                 }                 else                {                      break;                }                 if  (Operators.empty ())                  {                     printf ("Infix  Expression is invalid! ");                 }             }while (1);         }        else         {            do             {                 tmp = operators.pop ();       &nBsp;         operations.push (TMP);             }while (op  priority is less than  operators.top ());             operators.push (OP);         }    }    else    {         printf ("infix expression is invalid!");     }}while (!operators.empty ()) {    tmp = operators.pop ();     operations.push (TMP);} while (!operations.empty ()) {    tmp = operations.pop ();     printf (TMP);}

expression evaluation and conversion algorithm