If A is coded as C, M as I, N as P, S as O, I as A, P as N, E as M, O as E and…

Concept

In a direct substitution code, each source symbol has one fixed replacement. The order of the symbols does not change; each symbol is replaced independently.

To encode a word, scan it from left to right and apply the given source-to-code mapping at every position.

Application

Apply the supplied mapping to the nine letters of COMPANIES in order:

1. C maps to S.

2. O maps to E.

3. M maps to I.

4. P maps to N.

5. A maps to C.

6. N maps to P.

7. I maps to A.

8. E maps to M.

9. S maps to O.

Cross-check

The encoded string has nine symbols, matching the nine letters in the source word. Applying the inverse mapping to S–E–I–N–C–P–A–M–O returns C–O–M–P–A–N–I–E–S.

Therefore, the code for COMPANIES is SEINCPAMO.