[Twenty Eleven] How can I add "Continue reading…" automatcally?

On the index.php you could change the_content to the_excerpt.

do you mean you want to use ‘the_excerpt’ function instead of ‘the_content’?
https://codex.www.ads-software.com/Function_Reference/the_excerpt

in your child theme, edit content.php, and change this line:

<?php if ( is_search() ) : // Only display Excerpts for Search ?>

for instance to:

<?php if ( is_search() || is_home() ) : // Only display Excerpts for Search & blog page ?>

https://codex.www.ads-software.com/Conditional_Tags

Thank you both. I followed the alchymyth‘s suggestion and it worked like a charm. Thanks.

But is there any way so that I can change the number of the character displayed before ‘Continue Reading …’ button? The default number of character is too less for me. Using to this information, I tried to change the default number of characters by adding the following codes in my child theme’s function.php

function new_excerpt_length($length) {
	return 20;
}
add_filter('excerpt_length', 'new_excerpt_length');

But it doesn’t work. (I am not a coder/programmer, so I am not sure whether I did it right).

it is a bit complicated, because functions.php of the child theme gets executed before the one of the parent theme; thereofre your filter gets overwritten by the original filter for the excerpt length.

one way to do it:
add a higher priority to the new filter (https://codex.www.ads-software.com/Function_Reference/add_filter);

example:

function new_excerpt_length($length) {
	return 20;
}
add_filter('excerpt_length', 'new_excerpt_length', 11);

———–
different way to do it:

remove the original filter (after the theme setup) and add your own (you are generally on the right track);

example:

add_action( 'after_setup_theme', 'twentyeleven_child_change_excerpt_length' );
function twentyeleven_child_change_excerpt_length() {
  remove_filter('excerpt_length', 'twentyeleven_excerpt_length' );
  add_filter( 'excerpt_length', 'twentyeleven_child_excerpt_length' );
}
function twentyeleven_child_excerpt_length( $length ) {
	return 20;
}

Thanks alchymyth. It seems much complicated for me, though I’ll try. Thanks again! ??