Infix expression detects and converts a suffix expression, computes the result of a suffix expression

The implementation code is as follows

#include <iostream> #include <stack> #include <ctype.h>using namespace std;//The number here is only one//scan expression is legal, Legal return 0, otherwise return non 0int Scanner (const char *str) {stack<char*> s;if (str==null) {return-1;} Char *p= (char*) str;while (*p!= ') {if (*p== ' (')//If the left parenthesis is in the stack {s.push (p);} else if (*p== ') ')//right parenthesis to get the stack top symbol and match {if (!s.empty ())//Stack not empty {char *t=s.top ();//Get stack top element to match if (*t== ' (')//Match {s.pop ();}}} p++;} if (!s.empty ())//Last stack is empty match failed {return-1;} return 0;} Returns the priority of an operation symbol int getpriority (char ch) {if (ch== ' + ' | | ch== '-') {return 1;} else if (ch== ' * ' | | ch== '/') {return 2;} Else{return 0;}} Infix expression converted to postfix expression int Transform (/*in*/char *src,/*out*/char *dest) {stack<char*> s;int i=0;if (src==null| | Dest==null) {return-1;} Char *psrc=src;while (*psrc!= ') {//if (*psrc>= ' 0 ' && *psrc<= ' 9 ')//If it is a number if (IsDigit (*PSRC))//If the character is a number {dest[i]=*psrc;i++;} else if (*psrc== ')//If the left parenthesis is in the stack {s.push (PSRC);} else if (*psrc== ') ')//If it is a closing parenthesis, pop up the top element of the stack {while (!s.empty () && (*s.top ())! = ' (') {dest[i]=*s.top (); I++;s.pop ();} S.pop ();//pop-up opening parenthesis}else if (*psrc==' + ') | | (*psrc== '-') | | (*psrc== ' * ') | | (*psrc== '/')) If it is operator {while (!s.empty () &&getpriority (*s.top ()) >=getpriority (*PSRC))//comparison operator precedence {//if stack top symbol priority is not low dest[i] =*s.top (); I++;s.pop ();} S.push (PSRC);//stack top symbol priority low}else{cout<< "there are illegal characters in the expression" <<endl;return-1;} psrc++;} while (!s.empty ()) {dest[i]=*s.top (); I++;s.pop ();} dest[i]= ' + ';//The last character ends with a. return 0;} algorithm int arithmetic (int left,int right,char c) {switch (c) {case ' + ': return left+right;case '-': return left-right;case ' * ': Return left*right;case '/': if (right==0) {return 0;} Else{return Left/right;} Default:return 0;}} Computes the result of the operation of the suffix expression//Description This interface returns the result, not very good, the result can be outgoing, using a first-level pointer//int calculate (char *str,int* out) int calculate (char *src) {if (src== NULL) {return-1;} stack<int> s;//stack into intchar* psrc=src; The result of an int result=0;//expression evaluates while (*psrc!= ' s) {if (IsDigit (*PSRC))//If the character is a number {S.push (*psrc-' 0 ');//Converts the number symbol to int into the stack}else if ((*psrc== ' + ') | | (*psrc== '-') | | (*psrc== ' * ') | | (*psrc== '/')) If it is the symbol {int right=s.top ();//Get left operand and eject s.pop (); int left=s.top ();//Get right operand and pop s.pop (); int Re=ariThmetic (LEFT,RIGHT,*PSRC); S.push (re);//Press the result of the operation into the stack}else{cout<< "there are illegal characters in the expression" <<endl;return-1;} psrc++;} if (S.size () ==1)//The stack has only one result, which is the result of the final operation {result=s.top (); return Result;//s.pop ();} else{cout<< "Operation result is incorrect" <<endl;return-1;} return result;} int main () {char *exp= "(2+4) *3-9";cout<< "infix expression:" <<exp<<endl;if (Scanner (exp)!=0) {printf ("Expression match failed \ n "); return-1;} Char newexp[128]; Transform (exp,newexp);cout<< "suffix expression:" <<newexp<<endl;int re=calculate (newexp);cout<< " The result of the operation is: "<<re<<endl;return 0;}

　　

Infix expression detects and converts a suffix expression, computes the result of a suffix expression