表达式求值

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http://acm.nyist.net/JudgeOnline/problem.php?pid=35

 #include<bits/stdc++.h>using namespace std;const int N=1e3+7;const int inf=0x3f3f3f3f;char str[N];stack<double> num;stack<char> op;int priority(char c){    if(c=='+') return 1;    if(c=='-') return 1;    if(c=='*') return 2;    if(c=='/') return 2;    return 0;}void calculate(){    double b=num.top();num.pop();    double a=num.top();num.pop();    switch(op.top())    {        case '+': num.push(a+b);break;        case '-': num.push(a-b);break;        case '*': num.push(a*b);break;        case '/': num.push(a/b);break;    }    op.pop();}int main(){    int i,j,t,n,m,tt=0;    scanf("%d",&t);    while(t--)    {        scanf("\n%s",&str);        while(!op.empty()) op.pop();        while(!num.empty()) num.pop();        int len=strlen(str);        for(i=0;i<len;i++)        {            if(isdigit(str[i]))            {                double tmp;                sscanf(str+i,"%lf%n",&tmp,&n);                i+=(n-1);                num.push(tmp);            }            else if(str[i]=='(') op.push(str[i]);            else if(str[i]==')')            {                while(op.top()!='(') calculate();                op.pop();            }            else if(op.empty()||priority(str[i])>priority(op.top())) op.push(str[i]);            else            {                while(!op.empty()&&priority(str[i])<=priority(op.top()))calculate();                op.push(str[i]);            }        }        op.top();        printf("%.2lf\n",num.top());        num.pop();    }    return 0;}

http://acm.nyist.net/JudgeOnline/problem.php?pid=1272

 #include<bits/stdc++.h>using namespace std;const int N=1e3+7;const int inf=0x3f3f3f3f;char str[N];stack<int> num;stack<char> op;int priority(char c){    if(c=='*') return 2;    if(c=='+') return 1;    return 0;}void calculate(){    int suma=0,sumb=0;    int b=num.top();num.pop();    int a=num.top();num.pop();    switch(op.top())    {        case '+': num.push(a+b);break;        case '*': num.push(a*b);break;        case 'S': while(b!=0) sumb+=b%10,b/=10;                  while(a!=0) suma+=a%10,a/=10;                  num.push(max(suma,sumb));break;    }    op.pop();}int main(){    int i,j,t,n,m,tt=0,tmp;    scanf("%d",&t);    while(t--)    {        scanf("\n%s",&str);        while(!op.empty()) op.pop();        while(!num.empty()) num.pop();        int len=strlen(str);        for(i=0;i<=len;i++)        {            if(isdigit(str[i]))            {                sscanf(str+i,"%d%n",&tmp,&n);                i+=(n-1);                num.push(tmp);            }            else if(str[i]=='(') op.push(str[i]);            else if(str[i]==')')            {                while(op.top()!='(') calculate();                op.pop();            }            else if(str[i]=='S')            {                op.push('(');op.push('S');                i+=4;            }            else if(str[i]==',') {}            else if(op.empty()||priority(str[i])>priority(op.top())) op.push(str[i]);            else            {                while(!op.empty()&&priority(str[i])<=priority(op.top()))                    calculate();                op.push(str[i]);            }        }        printf("%d\n",num.top());    }    return 0;}

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