使用堆栈反转字符串

Question

I have a problem with reversing string using stack structure.

I made some code to reverse 'apple' to 'elppa' and seems like it worked well...

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

#define MAX_STACK_SIZE 5

typedef int element;

element stack[MAX_STACK_SIZE];

int top = -1;

void initialize() {
    top = -1;
}

int isEmpty() {
    return (top == -1);
}

int isFull() {
    return (top == (MAX_STACK_SIZE - 1));
}

void push(element item) {
    if (isFull()) {
        printf("stack is full, cannot add element.\n");
    }
    else{
        stack[++top] = item;
    }
}

element pop() {
    if (isEmpty()) {
        printf("stack is empty\n");
    }
    else {
        return stack[top--];
    }
}

char* reverse(char* s) {
    const int len = sizeof(s) + 1;
    char* rstring = new char[len];
    initialize();
    for (int i = 0; i < len; i++) {
        push(s[i]);
    }
    int tmp = 0;
    while(isEmpty()==false){
        rstring[tmp++]=pop();
    }
    for (int i = 0; i < len; i++) {
        printf("%c\n", rstring[i]);
    }
    return rstring;
}

void main() {
    char* str1 = "apple";
    char* str2 = reverse(str1);

    printf("before : %s \n", str1);
    printf("after : %s \n", str2);
    getchar();
}

the result is here I got the answer(elppa) but it also printed out some other characters what I wasn`t intended. Why I got this thing? It may something to do with memory array or something but do not know exactly what was happened memory. How to fix the problem?

Answer 1

You haven't taken into account the string termination character '\\0' . You are printing the sting using %s with printf.

Once rstring has been calculated after unwinding the stack, you should append '\\0' to rstring. Hopefully this will solve your problem.

Answer 2

By using sizeof you will get the data_type size (in this case, size of char*) in bytes. You should use strlen instead.