How do I find out if a program is running in "C" (this is linux)

[n_techo]

In bash I can find out if a program is running and do stuff if it is running or not running

the code in bash

if [ `pstree | grep -o "progname" | head -n 1` = "progname" ]; then

echo "program is running"

else

echo "program is not running"

fi

How do I do the same thing in "C"

Thanks