堆栈实现，计算后缀表达式

/*compute sufix expression*/#include <stdio.h>#include "stack.h"#include <string.h>#include <assert.h>#include <ctype.h>#define TRUE1#define FASLE0double add( double op1, double op2 );double sub( double op1, double op2 );double mul( double op1, double op2 );double div( double op1, double op2 );static char operator_group[] = "+-*/";static double (*op[4])( double , double ) = {add, sub, mul, div};int is_operator( char ch );static char whitespace[] = " \t\f\v\n\r";#define MAX_LEN100int main(){doublecmp_temp1, cmp_temp2, cmp_result;doubleulti_result;char*token;charbuffer[MAX_LEN];printf("Please input the expression\n");while( fgets( buffer, MAX_LEN, stdin ) != NULL ){for( token = strtok( buffer, whitespace);token != NULL;token = strtok( NULL, whitespace ) ){if( is_operator( *token ) && *(token + 1) == '\0' ){cmp_temp2 = top();pop();cmp_temp1 = top();pop();switch( *token ){case '+':cmp_result = op[0]( cmp_temp1, cmp_temp2 );break;case '-':cmp_result = op[1]( cmp_temp1, cmp_temp2 );break;case '*':cmp_result = op[2]( cmp_temp1, cmp_temp2 );break;case '/':cmp_result = op[3]( cmp_temp1, cmp_temp2 );break;}push( cmp_result );}else {floatf_value;sscanf(token ,"%f", &f_value );push( f_value );}}}/*打印结果*/ulti_result = top();pop();//堆栈应该为空；assert(is_empty())printf("the result of the expression is %f", ulti_result );return 0;}int is_operator(  char ch  ){char*ptr = &ch;if( strpbrk( ptr, operator_group ) == NULL )return FASLE;return TRUE;}double add( double op1, double op2 ){return op1 + op2;}double sub( double op1, double op2 ){return op1 - op2;}double mul( double op1, double op2 ){return op1 * op2;}double div( double op1, double op2 ){if( op2 == 0 ){printf( "除数不能为0" );return FASLE;}return op1 / op2;}

计算后缀表达式；

可以计算浮点数，负数，没有添加其他的运算符，只有+-*/