题解 | #表达式求值#

思路

哈哈哈，这是做了个计算器啊

代码是copy牛友的，，，
学下栈知识再来刷

Answer

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
char* ToNPL(char* s)
{
    char* NPL=(char*)malloc(sizeof(char)*(201));
    char* stack=(char*)malloc(sizeof(char)*strlen(s));
    int top=-1;
    int size=0;
    for(int i=0;i<strlen(s);i++)
    {
        if(s[i]>='0' && s[i]<='9')
        {
            NPL[size++]=s[i];
        }
        else
        {
            if(size>0)
            {
                if(NPL[size-1]!=' ')
                {
                    NPL[size++]=' ';
                }
                
            }
            if(top==-1)
            {
                stack[++top]=s[i];
            }
            else if(s[i]=='(')
            {
                stack[++top]=s[i];
            }
            else if((s[i]=='*' || s[i]=='/')&&(stack[top]=='+' || stack[top]=='-'))
            {
                stack[++top]=s[i];
            }
            else if(stack[top]=='(')
            {
                stack[++top]=s[i];
            }
            else if(s[i]==')')
            {
                while(stack[top]!='(')
                {
                    NPL[size++]=stack[top--];
                    NPL[size++]=' ';
                }
                top--;
            }
            else if(s[i]=='+' || s[i]=='-')
            {
                while(top!=-1)
                {
                    if(stack[top]=='(')
                    {
                        break;
                    }
                    NPL[size++]=stack[top--];
                    NPL[size++]=' ';
                }
                stack[++top]=s[i];
            }
            else if(s[i]=='*' || s[i]=='/')
            {
                while(top!=-1)
                {
                    if(stack[top]=='+' || stack[top]=='-' || stack[top]=='(')
                    {
                        break;
                    }
                    NPL[size++]=stack[top--];
                    NPL[size]==' ';
                }
                stack[++top]=s[i];
            }
        }
    }
    if(NPL[size-1]!=' ')
    {
        NPL[size++]=' ';
    }
    while(top!=-1)
    {
        NPL[size++]=stack[top--];
        NPL[size++]=' ';
    }
    NPL[size-1]='\0';
    free(stack);
    return NPL;
}

int caculate(char* s)
{
    int* stack=(int*)malloc(sizeof(int)*100);
    int top=-1;
    for(int i=0;i<strlen(s);i++)
    {
        if(s[i]>='0' && s[i]<='9')
        {
            int j=i;
            char* temp=(char*)malloc(sizeof(char)*100);
            while(s[j]!=' ')
            {
                temp[j-i]=s[j];
                j++;
            }
            temp[j-i]='\0';
            i=j;
            int num=atoi(temp);
            free(temp);
            stack[++top]=num;
        }
        else if(s[i]=='+')
        {
            int temp1=stack[top--];
            int temp2=stack[top--];
            int temp3=temp2+temp1;
            stack[++top]=temp3;
        }
        else if(s[i]=='-')
        {
            int temp1=stack[top--];
            int temp2=stack[top--];
            int temp3=temp2-temp1;
            stack[++top]=temp3;
        }
        else if(s[i]=='*')
        {
            int temp1=stack[top--];
            int temp2=stack[top--];
            int temp3=temp2*temp1;
            stack[++top]=temp3;
        }
        else if(s[i]=='/')
        {
            int temp1=stack[top--];
            int temp2=stack[top--];
            int temp3=temp2/temp1;
            stack[++top]=temp3;
        }
        
    }
    int ans=stack[top--];
    free(stack);
    return ans;
}
int main()
{
    char* str=(char*)malloc(sizeof(char)*101);
    scanf("%s\n",str);
    char* str_process=(char*)malloc(sizeof(char)*201);
    int size=0;
    for(int i=0;i<strlen(str);i++)
    {
        if(str[i]=='-')
        {
            if(i==0)
            {
                str_process[size++]='0';
                str_process[size++]=str[i];
            }
            else if(str[i-1]==')')
            {
                str_process[size++]=str[i];
            }
            else if(str[i-1]<'0' || str[i-1]>'9')
            {
                str_process[size++]='0';
                str_process[size++]=str[i];
            }
            else
            {
                str_process[size++]=str[i];
            }
        }
        else
        {
            str_process[size++]=str[i];
        }
    }//给负数补0
    str_process[size]='\0';
    char* str_NPL=ToNPL(str_process);//将中缀表达式改为后缀表达式
    int str_ans=caculate(str_NPL);//计算后缀表达式
    printf("%d\n",str_ans);
    free(str_NPL);
    free(str_process);
    return 0;
    
}