前后缀表达式c语言代码

前缀表达式：

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

#define MAX_SIZE 100

typedef struct stack {
    int top;
    int data[MAX_SIZE];
} Stack;

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

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

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

void push(Stack *s, int value) {
    if (is_full(s)) {
        printf("stack is full\n");
        return;
    }
    s->data[++s->top] = value;
}

int pop(Stack *s) {
    if (is_empty(s)) {
        printf("stack is empty\n");
        return -1;
    }
    return s->data[s->top--];
}

int peek(Stack *s) {
    if (is_empty(s)) {
        printf("stack is empty\n");
        return -1;
    }
    return s->data[s->top];
}

int evaluate_prefix_expression(char *expression) {
    Stack s;
    init(&s);

    int length = strlen(expression);
    for (int i = length - 1; i >= 0; i--) {
        if (isdigit(expression[i])) {
            push(&s, expression[i] - '0');
        } else {
            int operand1 = pop(&s);
            int operand2 = pop(&s);
            switch (expression[i]) {
                case '+':
                    push(&s, operand1 + operand2);
                    break;
                case '-':
                    push(&s, operand1 - operand2);
                    break;
                case '*':
                    push(&s, operand1 * operand2);
                    break;
                case '/':
                    push(&s, operand1 / operand2);
                    break;
                case '%':
                    push(&s, operand1 % operand2);
                    break;
                default:
                    printf("invalid character %c\n", expression[i]);
                    return -1;
            }
        }
    }
    return pop(&s);
}

int main() {
    char expression[MAX_SIZE];
    printf("Enter prefix expression: ");
    fgets(expression, MAX_SIZE, stdin);
    expression[strlen(expression) - 1] = '\0'; // remove newline character
    int result = evaluate_prefix_expression(expression);
    printf("Result = %d\n", result);
    return 0;
}

后缀表达式：

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

#define MAX_SIZE 100

typedef struct stack {
    int top;
    int data[MAX_SIZE];
} Stack;

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

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

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

void push(Stack *s, int value) {
    if (is_full(s)) {
        printf("stack is full\n");
        return;
    }
    s->data[++s->top] = value;
}

int pop(Stack *s) {
    if (is_empty(s)) {
        printf("stack is empty\n");
        return -1;
    }
    return s->data[s->top--];
}

int peek(Stack *s) {
    if (is_empty(s)) {
        printf("stack is empty\n");
        return -1;
    }
    return s->data[s->top];
}

int evaluate_postfix_expression(char *expression) {
    Stack s;
    init(&s);

    int length = strlen(expression);
    for (int i = 0; i < length; i++) {
        if (isdigit(expression[i])) {
            push(&s, expression[i] - '0');
        } else {
            int operand2 = pop(&s);
            int operand1 = pop(&s);
            switch (expression[i]) {
                case '+':
                    push(&s, operand1 + operand2);
                    break;
                case '-':
                    push(&s, operand1 - operand2);
                    break;
                case '*':
                    push(&s, operand1 * operand2);
                    break;
                case '/':
                    push(&s, operand1 / operand2);
                    break;
                case '%':
                    push(&s, operand1 % operand2);
                    break;
                default:
                    printf("invalid character %c\n", expression[i]);
                    return -1;
            }
        }
    }
    return pop(&s);
}

int main() {
    char expression[MAX_SIZE];
    printf("Enter postfix expression: ");
    fgets(expression, MAX_SIZE, stdin);
    expression[strlen(expression) - 1] = '\0'; // remove newline character
    int result = evaluate_postfix_expression(expression);
    printf("Result = %d\n", result);
    return 0;
}