Problem with File Descriptor Handling in a C Command Line Interpreter Using Pipes

I'm building a simple command line interpreter in C, and I've encountered an issue with handling file descriptors when using pipes. The interpreter is supposed to support piped commands, but I'm running into problems with closing file descriptors correctly. Here’s a snippet of the main loop that executes commands:

for (i = 0; i < params.cnt_prog; i++) {
    len = proc_len(lst);
    char* buf[len + 1];
    lst2buf(&lst, buf);
    buf[len] = NULL;

    if (i < params.cnt_prog - 1) {
        pipe(i % 2 == 0 ? fd1 : fd2);
    }

    pid = fork();
    if (pid == 0) {
        /* Set child input */
        if (i > 0) { 
            if (i % 2 == 1) { 
                dup2(fd1[0], 0);
                close(fd1[0]);
                close(fd1[1]);
            } else {
                dup2(fd2[0], 0);
                close(fd2[0]);
                close(fd2[1]);
            }
        } else {
            close(fd1[0]);
            if (!redirect_in(&params)) {
                exit(1);
            }
        }

        /* Set output */
        if (i < params.cnt_prog - 1) { 
            if (i % 2 == 1) {
                dup2(fd2[1], 1);
                close(fd2[1]);
                close(fd2[0]);
            } else {
                dup2(fd1[1], 1);
                close(fd1[1]);
                close(fd1[0]);
            }
        } else {
            close(fd1[1]);
            close(fd2[1]);
            if (!redirect_out(&params)) 
                exit(1);
        } 

        execvp(buf[0], buf);
        perror(buf[0]);
        exit(1);
    }

    if (i > 0) {
        if (i % 2 == 1) {
            close(fd1[0]);
            close(fd1[1]);
        } else {
            close(fd2[0]);
            close(fd2[1]);
        }
    }
}

• params.cnt_prog is the number of commands in the pipeline (e.g., ls | grep ".c" has 2 commands), executed from command line (ls | grep ".c" will produce 2)
• I’m confident that the logic converting the list to an array (lst2buf) is correct, so the problem likely lies with how I'm managing the pipe file descriptors in the parent and child processes.

Output examples:

> ls | grep .c
grep: (standard input): Bad file descriptor

> cat main.c | wc
wc: 'standard input': Bad file descriptor
0 0 0
wc: -: Bad file descriptor