//表达式转换//中缀转后缀
//从左往右扫描，从表达式前面开始扫描
//左括号入栈，右括号一直出栈，碰到右括号停下来
//栈顶运算符小于等于扫描到的运算符则出栈，写入表达式
void infixToPostfix(char infix[], char s2[], int &top2)
{char s1[maxSize]; int top1 = -1;//s1辅助栈，s2是结果栈int i = 0;while(infix[i] != '\0'){if('0' <= infix[i] && infix[i] >= '9'){s2[++top2] = infix[i];++i;}else if(infix[i] == '('){s1[++top1] = infix[i];++i;}else if(infix[i] == '+' ||infix[i] == '-' ||infix[i] == '*' ||infix[i] == '/' ){if(top1 == -1 ||s1[top1] == '(' ||getPriority(infix[i]) > getPriority(s1[top1])){s1[++top1] = infix[i];++i;}elses2[++top2] = s1[top1--];}else if (infix[i] == ')'){while(s1[top1] == '(')s2[++top2] = s1[top1--];--top1;++i;}while(top1 != -1)s2[++top2] == s1[top1--];}
}//中缀转前缀
//从右往左扫描，也就是从后开始扫描
//右括号入栈，碰到左括号停下来
//栈顶运算符小于扫描到的运算符出栈，写入表达式
void infixToPrefix(char infix[], int len, char s2[], int &top2)
{char s1[maxSize]; int top1 = -1;//s1辅助栈，s2是结果栈int i = len - 1;while(i >= 0){if('0' <= infix[i] && infix[i] >= '9'){s2[++top2] = infix[i];--i;}else if(infix[i] == ')'){s1[++top1] = infix[i];--i;}else if(infix[i] == '+' ||infix[i] == '-' ||infix[i] == '*' ||infix[i] == '/' ){if(top1 == -1 ||s1[top1] == ')' ||getPriority(infix[i]) >= getPriority(s1[top1])){s1[++top1] = infix[i];--i;}elses2[++top2] = s1[top1--];}else if (infix[i] == '('){while(s1[top1] == ')')s2[++top2] = s1[top1--];--top1;--i;}while(top1 != -1)s2[++top2] == s1[top1--];}
}
//后缀转前缀
//扫描到的运算符，移动到出栈2个子表达式的前面