Brackets check

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

int st(char str[])
    {
        int j, k = 0;
        char* st = (char*)malloc(sizeof(char)*strlen(str));
        for (j = 0; j!= strlen(str); j++)
        {
            switch (str[j])
            {
                case '(':
                    st[k] = '(';
                    k++;
                    break;
                case '{':
                    st[k] = '{';
                    k++;
                    break;
                case '[':
                    st[k] = '[';
                    k++;
                    break;
                case ')':
                    if( (st[k-1] == '(') )
                        k--;
                    else
                    {
                        free(st);
                        return 0;
                    }
                    break;
                case '}':
                    if( (st[k-1] == '{') )
                    k--;
                    else
                    {
                        free(st);
                        return 0;
                    }
                    break;
                case ']':
                    if( (st[k-1] == '[') )
                    k--;
                    else
                    {
                        free(st);
                        return 0;
                    }
                    break;
            }
        }
        if (k== 0)
            return 1;
        else
            {
                free(st);
                return 0;
            }
    }



int main()
{
    int i, j, z, brackets = 0;
    char c, *str = "", *tmp = NULL;

    for (i=0; (c = getchar())!= '\n'; i++)
    {
        tmp = str;
        str = (char*)malloc(i+2);
        strcpy(str, tmp);
        free(tmp);
        str[i] = c;
        str[i+1]= '\0';
    }
    for (i = 0; i< strlen(str); i++)
    if ((str[i] == '(') || (str[i] == '{') || (str[i] == '[') || (str[i] == ')') || (str[i] == '}') || (str[i] == ']'))
        brackets++;
    if (brackets == 0)
    {
        printf("There are no brackets\n");
        return 0;
    }
    if (st(str) == 1)
        printf("Everythig is OK\n");
    else
        printf("Smt is wrong\n");
    free(str);
    return 0;
}