20. Valid Parentheses

#define STACK_SIZE  10000
struct stack{
        char a[STACK_SIZE];
        int top;
};
void push(struct stack *s, char c)
{
        if(s->top == STACK_SIZE-1)
                return;
        else{
                s->top++;
                s->a[s->top] = c;
        }

}

char pop(struct stack *s)
{
        if(s->top == -1)
                return -1;
        else{
            
                return s->a[s->top--];
        }
}

bool isValid(char* s) {
        struct stack stack;
        stack.top = -1;
        char c;
        int tag = 0;

        while(*s != '\0'){
                printf("%c tag = %d\n", *s, tag);
                if(*s == '(' || *s == '{' || *s == '['){
                        push(&stack, *s);
                        s++;
                        tag++;
                }
                else if(*s == ')' || *s == '}' || *s == ']'){
                        c = pop(&stack);
                        printf("c = %c\n", c);
                        if(c == '(' && *s == ')')
                                tag--,s++;
                        else if(c == '{' && *s == '}')          
                                tag--,s++;
                        else if(c == '[' && *s == ']')
                                tag--,s++;
                        else
                                return false;
                }else
                        s++;

        }
 if(tag == 0)
            return true;
    else
            return false;
}