C- Character Push and Pop operation [closed]

问题

Stack create(int c)
{
    Stack S=(Stack)malloc(sizeof(struct stack));

    S->size=c;
    S->top=-1;
    S->array=(char *)malloc(sizeof(char)*c);

    return S;
}

Stack makeEmpty(void)
{
    Stack *S1=create(100);
    S1[0]->top=-1;
    return S1;
}

char pop(Stack S)
{
    return S->array[S->top--];
};

int main(void)
{
    Stack *S1;
    S1=makeEmpty();
    int j;
    int k=0;
    char result[30];
    for(j=0; j<2; j++)
    {
        char result1=pop(S1);
        strcat(result, result1);
        k++;
    }
}

I skipped some parts, like typedef struct stack Stack; What I wanted to do was pop out elements from the stack while for-loop works. Then, store those elements in a new array which is result. To check whether it works or not, I printed out but I had a runtime error. How to store the element and how to print it out?

回答1:

I've made copy&paste of your code, and it doesn't get compiled. I think that you are either not posting your actually code nor you don't bother to compile and read the compiler warnings. It's rather difficult to help you. Here some things I noticed:

1. create must return a pointer to Stack, not the object.

Stack *create(int c)
{
    Stack *S = malloc(sizeof *S);

    S->size=c;
    S->top=-1;
    S->array = malloc(c);

    return S;
}

2. Same goes for makeEmpty

Stack *makeEmpty(void)
{
    Stack *S1=create(100);
    S1->top=-1;
    return S1;
}

3. pop should get a pointer to Stack, not the object

char pop(Stack *S)
{
    return S->array[S->top--];
};

Here you should check whether there are elements on your stack. int pop(Stack *S, char *val) where it returns 1 and writes on *val on success, and returns 0 otherwise would be better.

4. Judging from your pop you are pushing char only. I don't get what you are trying to do with strcat. Either way, you are doing strcat wrong. You are declaring a stack with 100 spaces, but you are only declaring 30 spaces for result. What if you have more than 31 elements on your stack? I know that you are only inspecting 2 elements but it's easy to overlook that and expand it to go through all the stack without changing the memory requirements for result.

Also strcat is a function that works with C-Strings, that means it expects C-Strings. A C-String must be \0 terminated, yours are not. You have something that looks like a C-String but it's not. If you insist on using strcat, the you should do it like this:

for(j=0; j<2; j++)
{
    char result1[] = { pop(S1), 0 };
    strcat(result, result1);
}

来源：https://stackoverflow.com/questions/48069933/c-character-push-and-pop-operation

标签

arrays

stack

strcat