Implementing shell in C and need help handling input/output redirection

Round 2

After reading some of the answers, my revised code is:

int pid = fork();

if (pid == -1) {
    perror("fork");
} else if (pid == 0) {   

    if (in) { //if '<' char was found in string inputted by user
        int fd0 = open(input, O_RDONLY, 0);
        dup2(fd0, STDIN_FILENO);
        close(fd0);
        in = 0;
    }

    if (out) { //if '>' was found in string inputted by user
        int fd1 = creat(output, 0644);
        dup2(fd1, STDOUT_FILENO);
        close(fd1);
        out = 0;
    }   

    execvp(res[0], res);
    perror("execvp");
    _exit(1);
} else {
    waitpid(pid, 0, 0);
    free(res);
}

It works, but seems the standard output isn't being reconnected or something to that effect. Here is execution:

SHELL$ cat > file
hello, world
this is a test
SHELL$ cat < file //no output
SHELL$ ls //no output

'<' and '>' both work, but after they are executed there is no output.

Round 1

I have been working on a relatively simple shell in C for a while now, but I am having trouble implementing input (<) and output (>) redirection. Help me find the issues in the following code:

int fd;
int pid = fork();
int current_out;

if (in) { //if '<' char was found in string inputted by user
    fd = open(input, O_RDONLY, 0);
    dup2(fd, STDIN_FILENO);
    in = 0;
    current_out = dup(0);
}

if (out) { //if '>' was found in string inputted by user
    fd = creat(output, 0644);
    dup2(fd, STDOUT_FILENO);
    out = 0;
    current_out = dup(1);
}

if (pid == -1) {
    perror("fork");
} else if (pid == 0) {       
    execvp(res[0], res);
    perror("execvp");
    _exit(1);
} else {
    waitpid(pid, 0, 0);
    dup2(current_out, 1);
    free(res);
}

I may have some unnecessary material in there because I have been trying different things to get it to work. I am not sure what is going wrong.