C语言：任意算术表达式的求值

答案：#include <stdio.h> 
#include <conio.h>
#include <stdlib.h> 
#include <process.h> 
#include <string.h> 
#define N 100 
double numStack[N]={0}; 
int numTop; 
char opStack[N]; 
int opTop; 

int op(char ch) 
{ 
if(ch=='+'||ch=='-') return 2; 
if(ch=='*'||ch=='/') return 3; 
if(ch=='(') return -1; 
return 0; 
} 

double result(double num1,char op,double num2) 
{ 
if(op=='+') return num1+num2; 
if(op=='-') return num1-num2; 
if(op=='*') return num1*num2; 
if(op=='/') return num1/num2; 
return 0; 
} 

int compute(char str[]) 
{ 
double num=0; 
int i=0,j=1,k=1; 
int Flag=0; 
numTop=opTop=0; 
while(str[i]!='\0'||opTop>0) 
{ 
if(str[i]>='0'&&str[i]<='9') 
if(Flag==0) 
num=num*10+str[i]-'0'; 
else 
{ 
num+=(str[i]-'0')/(j*10.0); 
j*=10; 
} 
else 
if(str[i]=='.') 
Flag=1; 
else 
if( k==1&&str[i]=='-'&&(i==0||op(str[i-1])) ) 
k=-1; 
else 
{ 
if(i>0&&!op(str[i-1])&&str[i]!='('&&str[i-1]!=')') 
{ 
numStack[numTop++]=num*k; 
num=0; j=1; Flag=0; k=1; 
} 
if(opTop==0||str[i]=='(') 
opStack[opTop++]=str[i]; 
else 
if(str[i]==')') 
{ 
while(opTop>0&&opStack[--opTop]!='(') 
{ 
numStack[numTop-2]=result(numStack[numTop-2],opStack[opTop],numStack[numTop-1]); 
numTop--; 
} 
if(opStack[opTop]!='(') return 0; 
} 
else 
{ 
if(str[i]=='\0'&&numTop==0) return 0;
while(opTop>0&&op(str[i])<=op(opStack[opTop-1])) 
{ 
numStack[numTop-2]=result(numStack[numTop-2],opStack[--opTop],numStack[numTop-1]); 
numTop--; 
} 
if(str[i]!='\0') 
opStack[opTop++]=str[i]; 
} 
} 
if(str[i]!='\0') 
i++; 
} 
if(numTop!=1||opTop!=0) 
return 0; 
return 1; 
} 

void face() 
{ 
system("cls"); 
printf("__________________________________________________________________\n"); 
printf("  Save number(S) | Read number(R) | Clear(C) | Equal(E) | Quit(Q) \n"); 
printf("------------------------------------------------------------------\n"); 
} 

main() 
{ 
int i=0,j=0,k; 
char str[N]="\0"; 
char num[N]="\0"; 
char save[N]="\0"; 
char ch; 
double temp; 
unsigned long temp2; 
face(); 
printf("input an expression,press key 'E' to compute\n"); 
ch=getch(); 
while( 1 ) 
{ 
if(ch=='.'||ch==')'||op(ch)||ch>='0'&&ch<='9') 
{ 
str[i++]=ch; 
str[i]='\0'; 
face(); 
printf("input an expression,press key 'E' to compute\n"); 
printf("%s",str); 
if( ch=='-'&&(i==1||op(str[i-2]))||ch>='0'&&ch<='9' ) 
{ 
num[j++]=ch; 
num[j]='\0'; 
} 
else j=0; 
} 
if(ch=='S'||ch=='s') 
if(strlen(num)) 
{ 
face(); 
printf("%s has been saved\n",strcpy(save,num)); 
printf("input an expression,press key 'E' to compute\n"); 
printf("%s",str); 
} 
else 
{ 
face(); 
printf("there is no number to save!\n"); 
printf("input an expression,press key 'E' to compute\n"); 
printf("%s",str); 
} 
if(ch=='R'||ch=='r') 
if(strlen(save)) 
{ 
face(); 
printf("input an expression,press key 'E' to compute\n"); 
printf("%s",strcat(str,save)); 
i+=strlen(save); 
} 
if(ch=='C'||ch=='c') 
{ 
if(strlen(str)) 
str[--i]='\0'; 
face(); 
printf("input an expression,press key 'E' to compute\n"); 
printf("%s",str); 
} 
if(ch=='E'||ch=='e') 
{ 
if(compute(str)) 
{ 
printf("\n=%g\n",numStack[0]); 
j=0; temp=numStack[0]; 
if(temp<0) 
{ 
temp=-temp; 
num[j++]='-'; 
num[j]='\0'; 
} 
temp2=(unsigned long)temp; 
k=1; 
while(temp2/k>=10) 
k*=10; 
while(k) 
{ 
num[j++]=temp2/k+'0'; 
num[j]='\0'; 
temp2=temp2%k; 
k/=10; 
} 
temp=temp-(int)temp; 
if(temp!=0) 
{ 
num[j++]='.'; 
num[j]='\0'; 
temp+=0.0000005; 
} 
for(k=6;k>0;k--) 
{ 
if(temp==0) break; 
temp*=10; 
num[j++]=(int)temp+'0'; 
num[j]='\0'; 
temp=temp-(int)temp; 
} 
} 
else 
{ 
face(); 
printf("input an expression,press key 'E' to compute\n"); 
printf("%s",str); 
printf("\nwrong expression！"); 
} 
i=0; j=0; str[0]='\0'; 
} 
if(ch=='Q'||ch=='q') 
{ 
printf("\nare you sure to quit?（Y/N）\n"); 
ch=getch(); 
if(ch=='Y'||ch=='y') break; 
else 
{ 
face(); 
printf("input an expression,press key 'E' to compute\n"); 
printf("%s",str); 
} 
} 
ch=getch(); 
} 
}#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define MAX 50
int i = 0;
int judge_char( char ch );
int char_priority( char ch );
int judeg_number( char ch );
int conversion_char( char *conversion_pointer );
int evaluetion( int item1, int item2, char ch );
int main( void )
{
 char array1[MAX]; //存储中缀表达式 
 char stack[MAX]; //存储符号的栈 
 int array2[MAX]; //存储后缀表达式 
 int j = -1; //array2[]下标 
 int top = 0; //栈的下标 
 int item1, item2;
 char ch;
 
 stack[0] = '='; //让栈最初为'='号 
 printf( "输入表达式:" );
 gets( array1 );
  
 while( array1[i] != '\0' && array1[i] != '=' ) 
 {
  if( judge_char( array1[i] ) == 1 ) //判断是否是符号 
  {
   //比如符号的优先级 
   if( char_priority( array1[i] ) > char_priority( stack[top] ) )
   {
    stack[++top] = array1[i++];
   }
    
   else
   { //如果当然的符号小于栈项的符号,那就退栈 
    while( char_priority( array1[i] ) <= char_priority( stack[top] ) )
      {
       ch = stack[top--];
       item1 = array2[j--];
       item2 = array2[j--];
       array2[++j] = evaluetion( item2, item1, ch );
      }
      stack[++top] = array1[i++];
   }
  }
  //判断是否是数字 
  else if( ( judeg_number( array1[i] ) ) == 1 )
  {
   array2[++j] = conversion_char( array1 );
  }
   
  else if( array1[i] == '(' ) //如果是左括,直接进入 
  {
   stack[++top] = array1[i++];
  }
   
  else if( array1[i] == ')' ) //如果是右括,那就输出栈中左括前的符号 
  {
   while( stack[top] != '(' )
   {
    ch = stack[top];
    item2 = array2[j--];
    item1 = array2[j--];
    array2[++j] = evaluetion( item1, item2, ch );
    top--;
   }
    i++;
    top--;
  }
  
 }
  
 while( top > 0 )
 {
  ch = stack[top--]; //如果栈中还有符号,就完退栈 
  item1 = array2[j--];
  item2 = array2[j--];
  array2[++j] = evaluetion( item2, item1, ch );
 }
 
 printf( "%d\n", array2[j] );
 return 0;
}
//判断符号 
int judge_char( char ch )
{
 switch( ch )
 {
  case '+' :
  case '-' :
  case '*' :
  case '/' : return 1;
  
  default : return 0;
 }
}
//判断符号优先级 
int char_priority( char ch )
{
 switch( ch )
 {
  case '+' :
  case '-' : return 1;
  
  case '*' : 
  case '/' : return 2;
  
  default : return 0;
 }
}
//判断字符数 
int judeg_number( char ch )
{
 if( ch >= '0' && ch <= '9' )
 {
  return 1;
 }
 else
 {
  return 0;
 }
}
//把字符转换为数字 
int conversion_char( char *conversion_pointer )
{
 char store_char[MAX] = { '\0' };
 int j = -1;
 int item;
 
 while( judeg_number( conversion_pointer[i] ) == 1 && conversion_pointer[i] != '\0' )
 {
  store_char[++j] = conversion_pointer[i];
  i++;
 }
 
 item
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