In middle / in the middle / in front / in the front

Can't we say, "in middle" like "in front"? For example,

"Put the expression in middle."

Or should we say, "Put the expression in the middle." And then, shouldn't we say, "in the front" instead of "in front" in the sentence,

"Put the expression in front."

Or is there a meaning difference between "in the middle" and "in middle" and "in the front" and in front"?

Thank you so much as always and I respect your precious opinions and time as usual.

"In middle" does not exist in English. It has to be "in the middle".

"In the front" is generally used with physical places. For example, "in the front of the store ... window ... house."

"In front" usually requires "of" unless the object is obvious from the context. For example we usually put the adjective in front of the noun.