Function to show excerpt

Php function
function news_excerpt($full_text, $letter_count = 50){

$full_text = trim($full_text);

$full_text = strip_tags($full_text);

$full_text = strip_shortcodes($full_text);

$full_text = mb_substr($full_text, 0, $letter_count);

$full_text = $full_text."...";

return $full_text;

}

Html
<?php echo news_excerpt(get_the_content(),100);?>