C语言表达式求值

RT
C或C++语言实现输入一个完整表达式，然后求值

除了使用数据结构的堆栈应用，能不能有其他方法实现这一功能？

//表达式求值
//By:jimly
//10/10/2009
//例如：输入2+2（4-6*3）=
//以"="结束,然后回车即出结果
#include <stdio.h>
#include <conio.h>
#include <windows.h>
#include <assert.h>
typedef float ElemType;
typedef struct Stack
{
ElemType *base; // 栈基址
ElemType *top; // 栈顶
int stacksize; // 栈存储空间的尺寸
} SqStack;

bool InitStack(SqStack *S);
bool InitStack(SqStack *S);
void DestroyStack(SqStack *S);
bool StackEmpty(SqStack S);
int StackLength(SqStack S);
ElemType GetTop(SqStack S, ElemType *e);
void StackTraverse(SqStack S, void (*fp)(ElemType));
bool Push(SqStack *S, ElemType e);
bool Pop(SqStack *S, ElemType *e);

char Precede(char A1,char A2);
ElemType Operate(ElemType a,ElemType theta,ElemType b);
bool In(char c,char op[]);
ElemType EvaluateExpression();
void Menu();

//////////////////////////////////////////////
// Eval_exdivssion.cpp 表达式求值实现函数 //
//////////////////////////////////////////////

char Precede(char A1,char A2)
{
if (A1 == '+' || A1 == '-')
{
if (A2 == '+' || A2 == '-' || A2 == ')' || A2 == '=')
{
return '>';
}
else
return '<';
}
if (A1 == '*' || A1 == '/')
{
if (A2 == '(')
{
return '<';
}
else
return '>';
}
if (A1 == '(')
{
if (A2 == ')')
{
return '=';
}
if (A2 == '=')
{
return 'E';
}
else
return '<';
}
if (A1 == ')')
{
if (A2 == '(')
{
return 'E';
}
if (A2 == '=')
{
return 'E';
}
else
return '>';
}
if (A1 == '=')
{
if (A2 == '=')
{
return '=';
}
else
return '<';
}
else
return '=';
}

ElemType Operate(ElemType a,ElemType theta,ElemType b)
{
switch(char(theta))
{
case '+':
return a += b;
break;
case '-':
return a -= b;
break;
case '*':
return a *= b;
break;
case '/':
if(b==0)
{
printf("除数不能为0！！\n");
exit(0);
}
return a /= b;
break;
}

return 0;
}

bool In(char c,char op[])
{
for (int i = 0;i<7;i++)
{
if (op[i] == c)
return true;
}
return false;
}

ElemType EvaluateExpression()
{
SqStack OPTR; //运算符栈
SqStack OPND; //运算数栈
char Ct = '='; //判断是否结束的标识
int i = 0,j = 1;
ElemType e = 0,t = 0,c;
char op[7] = {'+','-','*','/','(',')','='};

InitStack(&OPTR); //初始化
Push(&OPTR,Ct);
InitStack(&OPND); //初始化

c = (float)getchar();
while (c!='=' || GetTop(OPTR,&e)!='=')
{
if (!In((char)c,op)) //不是运算e符进栈
{
while(!In((char)c,op)) //可以是几位数
{
t = t*10+(c-48);
c = (float)getchar();
}
Push(&OPND,t);
t = 0;
}

else
{
switch (Precede((char)GetTop(OPTR,&e),(char)c))
{
case '<'://栈顶元素优先权低
Push(&OPTR,c);
c = (float)getchar();
break;
case '='://脱括号并接受下个字符
ElemType x;
Pop(&OPTR,&x);
c = (float)getchar();
break;
case '>'://退栈并将运算结果入栈
ElemType b,theta,a;
Pop(&OPTR,&theta);
Pop(&OPND,&b);
Pop(&OPND,&a);
Push(&OPND,Operate(a,theta,b));
break;
case 'E':
printf("括号不匹配！！\n");
exit(0);
break;

}
}
}
ElemType tem = GetTop(OPND,&e);
DestroyStack(&OPND);
DestroyStack(&OPTR);
return tem;
}

const int STACK_INIT_SIZE = 100; // 初始分配的长度
const int STACKINCREMENT = 10; // 分配内存的增量

bool InitStack(SqStack *S)
{
assert(S != NULL);
S->base = (ElemType *)malloc(sizeof(ElemType) * STACK_INIT_SIZE);

if(S->base == NULL) return false;

S->top = S->base;
S->stacksize = STACK_INIT_SIZE;

return true;
}

void DestroyStack(SqStack *S)
{
assert(S != NULL);

free(S->base);
S->top = S->base = NULL;
}

bool StackEmpty(SqStack S)
{
assert((S.base != NULL) && (S.top != NULL));
return(S.base == S.top);
}

int StackLength(SqStack S)
{
assert((S.base != NULL) && (S.top != NULL));
return(S.top-S.base);
}

ElemType GetTop(SqStack S, ElemType *e)
{
assert((S.base != NULL) && (S.top != NULL));
if(StackEmpty(S)) return false;

*e = *(S.top-1);
return *e;
}

void StackTraverse(SqStack S, void (*fp)(ElemType))
{
assert((S.base != NULL) && (S.top != NULL));
for(; S.base<S.top; S.base++) (*fp)(*S.base);
}

bool Push(SqStack *S, ElemType e)
{
if (S->top - S->base>=S->stacksize)
{
S->base = (ElemType *)realloc(S->base,(S->stacksize + STACKINCREMENT) * sizeof(ElemType));
if (!S->base)
exit(0);
S->top = S->base + S->stacksize;
S->stacksize += STACKINCREMENT;
}
*S->top++ = e;

return true;
}

bool Pop(SqStack *S, ElemType *e)
{
if(S == NULL) return false;
assert((S->base != NULL) && (S->top != NULL));
if(StackEmpty(*S)) return false;

*e = *(--S->top);
return true;
}

//////菜单///////
void Menu()
{
printf("表达式求值模拟程序\n\n");

printf("功能菜单：\n");
printf("==============\n");
printf("[1] 输入表达式并求值\n");
printf("[0] 退出 \n");
printf("==============\n");
printf("请输入你的选择(0~1)（以回车结束）：");
}

///////// 主函数 ///////////
//////////////////////////////
int main()
{
char ch = ' ',tp;

do
{
system("cls");
Menu();
ch = getchar();
if (ch == '0')
break;
tp = getchar();
printf("请输入一个表达式（最后输入”=“,然后回车出结果）：");
printf("这个表达式结果为：%g\n",EvaluateExpression());
tp = getchar();
printf("任意键继续...");
getch();
} while (true);

return 0;
}//end

实现表达式求值我是先将中缀表达式转换为后缀表达式，然后用堆栈实现求值的，

至于其他方法还没想过呢，期待有更好的方法吧。

按1输入表达式（不用输入＝号） 按2计算 按3输出结果 按4退出 程序如下： #include<stdio.h> #include <string.h> #include <conio.h> #define PLUS 0 #define MINUS 1 #define POWER 2 #define DIVIDE 3 #define LEFTP 4 #define RIGHP 5 #define STARTEND 6 #define DIGIT 7 #define POINT 8 #define NUM 7 #define NO 32767 #define STACKSIZE 20 char a[]={'+','-','*','/','(',')','#'}; int j,PriorityTable[7][7]={{ 1, 1,-1,-1,-1, 1, 1}, { 1, 1,-1,-1,-1, 1, 1}, { 1, 1, 1, 1,-1, 1, 1}, { 1, 1, 1, 1,-1, 1, 1}, {-1,-1,-1,-1,-1, 0, NO}, { 1, 1, 1, 1,NO, 1, 1}, {-1,-1,-1,-1,-1,NO, 0} }; int menu(void); void InputExpression(char str[]) { int len; printf("Input expression string:\n"); scanf("%s",str); len=strlen(str); str[len]='#'; str[len+1]='\0'; } int GetCharType(char ch) { int i; for(i=0;i<NUM;i++) if(ch==a[i]) return(i); if(ch>='0' && ch<='9') return(DIGIT); if(ch=='.') return(POINT); return(-1); } int EXCUTE(char *str,double *Result) { int pp,strlength,topTr,topNd,CharType,OPTR[STACKSIZE],a; double number,temp,OPND[STACKSIZE]; OPTR[0]=STARTEND; topTr=1; topNd=0; pp=0; while((str[pp])) { CharType=GetCharType(str[pp]); switch(CharType) { case -1: return(0); case DIGIT: number=0; while (str[pp]>='0' && str[pp]<='9') { number=number*10+(str[pp]-48); pp++; } if(str[pp]=='.') { temp=10.0; pp++; while(str[pp]>='0' && str[pp]<='9') { number=number+(str[pp]-48)/temp; temp=temp*10; pp++; } } OPND[topNd]=number; topNd++; break; case POINT: number=0; temp=10.0; pp++; while(str[pp]>='0' && str[pp]<='9') { number=number+(str[pp]-48)/temp; temp=temp*10; pp++; } OPND[topNd]=number;printf("%lf",number); topNd++; break; case PLUS: case MINUS: case POWER: case DIVIDE: {int i; i=PriorityTable[OPTR[topTr-1]][CharType]; if(i==-1) {OPTR[topTr]=CharType; topTr++; } if(i==1) {while(i==1) { j=OPTR[topTr-1]; if(j==0)OPND[topNd-2]=OPND[topNd-2]+OPND[topNd-1]; if(j==1)OPND[topNd-2]=OPND[topNd-2]-OPND[topNd-1]; if(j==2)OPND[topNd-2]=OPND[topNd-2]*OPND[topNd-1]; if(j==3)OPND[topNd-2]=OPND[topNd-2]/OPND[topNd-1]; topNd--; topTr--; i=PriorityTable[OPTR[topTr-1]][CharType]; } OPTR[topTr]=CharType;topTr++; } pp++;break; } case LEFTP: { OPTR[topTr]=LEFTP; topTr++;pp++; break; } case RIGHP: { while(1) if(OPTR[topTr-1]==LEFTP){topTr--;pp++;break;} else if(OPTR[topTr-1]==STARTEND)return(0); else {j=OPTR[topTr-1]; if(j==0)OPND[topNd-2]=OPND[topNd-2]+OPND[topNd-1]; else if(j==1)OPND[topNd-2]=OPND[topNd-2]-OPND[topNd-1]; else if(j==2)OPND[topNd-2]=OPND[topNd-2]*OPND[topNd-1]; else if(j==3)OPND[topNd-2]=OPND[topNd-2]/OPND[topNd-1]; topNd--; topTr--; } break; } case STARTEND: while(OPTR[topTr-1]!=STARTEND) { j=OPTR[topTr-1]; if(j==0)OPND[topNd-2]=OPND[topNd-2]+OPND[topNd-1]; else if(j==1)OPND[topNd-2]=OPND[topNd-2]-OPND[topNd-1]; else if(j==2)OPND[topNd-2]=OPND[topNd-2]*OPND[topNd-1]; else if(j==3)OPND[topNd-2]=OPND[topNd-2]/OPND[topNd-1]; topNd--; topTr--; } if(topNd==1) { *Result=OPND[0];return(1); } else return(0); } } return(1 ); } void main() { int num,flag; double result; char str[256]; str[0]=0; while(1) { num=menu(); switch(num) { case 1: InputExpression(str); flag=0; printf("%s\n",str); getchar(); getchar(); break; case 2: if(str[0]==0) { printf("Expresson is Empty!"); getchar(); break; } if(!EXCUTE(str,&result)) { printf("The expression has error!\n"); getchar(); } else { printf("calulation has finished!\n"); getchar(); flag=1; } break; case 3: if(flag) { printf("#%s=%lf\n",str,result); getchar(); getchar(); } break; case 4: break; } if(num==4) break; } } int menu(void) { int num; clrscr(); printf("%20c1--input expression\n",' '); printf("%20c2--calculation expression\n",' '); printf("%20c3--print result\n",' '); printf("%20c4--Quit\n",' '); printf(" please select 1,2,3,4:"); do{ scanf("%d",&num); }while(num<1 || num>4); return(num); }