话不多数代码如下，看不懂的同学请评论区留言哦

#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 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("请输入算术表达式:\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);
}
double Operate(double a,int theta,double b)
{
    double x;
    switch(theta)
    {
    case 0:
        x=a+b;
        break;
    case 1:
        x=a-b;
        break;
    case 2:
        x=a*b;
        break;
    case 3:
        x=a/b;
        break;
    }
    return (x);
}
int EXCUTE(char *str,double *Result)
{
    int pp,strlength,topTr,topNd,CharType,OPTR[STACKSIZE];
    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;
            topNd++;
            break;
        case PLUS:
        case MINUS:
        case POWER:
        case DIVIDE:
            if(PriorityTable[OPTR[topTr-1]][CharType]==-1)
            {
                OPTR[topTr]=CharType;
                topTr++;
                pp++;
            }
            else
            {
                OPND[topNd-2]=Operate(OPND[topNd-2],OPTR[topTr-1],OPND[topNd-1]);
                topNd--;
                topTr--;
            }
            break;
        case LEFTP:
            OPTR[topTr]=CharType;
            topTr++;
            pp++;
            break;
        case RIGHP:
            while(OPTR[topTr-1]!=LEFTP)
            {
                if(OPTR[topTr-1]==STARTEND)return(0);
                if(PriorityTable[OPTR[topTr-1]][CharType]==1)
                {
                    OPND[topNd-2]=Operate(OPND[topNd-2],OPTR[topTr-1],OPND[topNd-1]);
                    topNd--;
                    topTr--;
                }
                else
                    break;
            }
            topTr--;
            pp++;
            break;
        case STARTEND:
            while(OPTR[topTr-1]!=STARTEND)
            {
                OPND[topNd-2]=Operate(OPND[topNd-2],OPTR[topTr-1],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();
            break;
        case 2:
            if(str[0]=='0')
            {
                printf("表达式为空!");
                getchar();
                break;
            }
            if(!EXCUTE(str,&result))
            {
                printf("表达式有错!\n");
                getchar();
            }
            else
            {
                printf("计算结束!\n");
                getchar();
                flag=1;
            }
            break;
        case 3:
            if(flag)
            {
                printf("#%s=%lf\n",str,result);
                getchar();
            }
            break;
        case 4:
            break;
        }
        if(num==4) break;
    }
}
int menu(void)
{
    int num;
    printf("*----------1--输入表达式------------*\n",' ');
    printf("*----------2--计算表达式------------*\n",' ');
    printf("*----------3--输出结果--------------*\n",' ');
    printf("*----------4--退出------------------*\n",' ');
    printf("*----------请选择操作1,2,3,4--------:");
    do
    {
        scanf("%d",&num);
    }
    while(num<1 || num>4);
    return(num);
}