Apart from the missing 't' in the 2nd last line, there's no reason for this not to compile. That said, not really sure what it is you're trying to calculate here - I guess you're just getting the hang of the language, and playing around.
Given the use of the words length and perimeter & the /2 in the final calc, I've altered it slightly so that it calculates the perimeter of a rectangle (or square)
I also separated the printf/scanf pairs so that it's easier and more intuitive to use. Enjoy :)
int length, width, perim;
printf("Plz input length: ");
printf("\n Plz input width: ");
perim = (length + width) * 2;
printf("\n perimeter: %d", perim);