A C program is not a script; it is source code that must be compiled before use. You can compile the program and then invoke it from cron with its (fully qualified) name. For example, if you compile "test.c" to the executable "test", and place it in /usr/local/bin, your cron entry would be:
52 1 * * * /usr/local/bin/test
You should not place executables in the /etc directory; that is not where they belong. The /etc directory is for configuration parameters. Executables should be placed in a bin directory. Locally created executables that are available system-wide should be in /usr/local/bin/.