I can,t find how I do . in C programming

Example .

char time
time = system (date , 0);

*I will take the date like I type in shell "date" = Dinsdag 26-jun-2018 11.23.56

also command diskfree

Example .

int free
free = system (diskfree work: nopostfix , 0);

* Can somebody give a easy example to do that .