使用c语言实现

以下是使用C语言实现中缀表达式转后缀表达式的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_STACK_SIZE 100

typedef struct Stack {
    char data[MAX_STACK_SIZE];
    int top;
} Stack;

void init_stack(Stack *s) {
    s->top = -1;
}

int is_empty(Stack *s) {
    return s->top == -1;
}

int is_full(Stack *s) {
    return s->top == MAX_STACK_SIZE - 1;
}

void push(Stack *s, char c) {
    if (is_full(s)) {
        printf("Stack Overflow!\n");
        exit(1);
    }
    s->top++;
    s->data[s->top] = c;
}

char pop(Stack *s) {
    if (is_empty(s)) {
        printf("Stack Underflow!\n");
        exit(1);
    }
    char c = s->data[s->top];
    s->top--;
    return c;
}

char peek(Stack *s) {
    if (is_empty(s)) {
        printf("Stack Underflow!\n");
        exit(1);
    }
    return s->data[s->top];
}

int is_operator(char c) {
    return c == '+' || c == '-' || c == '*' || c == '/';
}

int precedence(char op) {
    if (op == '*' || op == '/') {
        return 2;
    } else if (op == '+' || op == '-') {
        return 1;
    } else {
        return 0;
    }
}

void infix_to_postfix(char *infix_expr, char *postfix_expr) {
    Stack op_stack;
    init_stack(&op_stack);

    int i = 0, j = 0;
    while (infix_expr[i] != '\0') {
        char c = infix_expr[i];
        if (c >= '0' && c <= '9' || c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z') {
            postfix_expr[j++] = c;
        } else if (c == '(') {
            push(&op_stack, c);
        } else if (c == ')') {
            while (peek(&op_stack) != '(') {
                postfix_expr[j++] = pop(&op_stack);
            }
            pop(&op_stack);
        } else if (is_operator(c)) {
            while (!is_empty(&op_stack) && is_operator(peek(&op_stack)) && precedence(peek(&op_stack)) >= precedence(c)) {
                postfix_expr[j++] = pop(&op_stack);
            }
            push(&op_stack, c);
        }
        i++;
    }

    while (!is_empty(&op_stack)) {
        postfix_expr[j++] = pop(&op_stack);
    }
    postfix_expr[j] = '\0';
}

int main() {
    char infix_expr[MAX_STACK_SIZE];
    char postfix_expr[MAX_STACK_SIZE];

    printf("Please enter an infix expression: ");
    fgets(infix_expr, MAX_STACK_SIZE, stdin);
    infix_expr[strlen(infix_expr) - 1] = '\0';

    infix_to_postfix(infix_expr, postfix_expr);

    printf("Postfix expression: %s\n", postfix_expr);

    return 0;
}

示例输入：

Please enter an infix expression: A + B * C + D / E

示例输出：

Postfix expression: ABC*+DE/+

上述代码中，我们使用了一个结构体Stack来定义栈，并实现了栈的基本操作函数。在infix_to_postfix函数中，我们遍历中缀表达式的每一个字符，如果是操作数，则直接加入后缀表达式中；如果是左括号，则入栈；如果是右括号，则弹出栈顶运算符并加入后缀表达式中，直到遇到左括号为止；如果是运算符，则比较其与栈顶运算符的优先级，如果栈顶的优先级高，则弹出栈顶运算符并加入后缀表达式中，直到栈顶运算符的优先级低于当前运算符，最后将当前运算符入栈。最后，将栈中剩余的运算符全部弹出并加入后缀表达式中。