BC/4.18 is a macro assembler produced by Teko Corporation in the 1980s, primarily used to develop software on IBM mainframes. It was similar to IBM's Assembler/H, but with more features, such as conditional assembly, macros, and a more modern syntax. The syntax was based on IBM's ASMx, an earlier version of Assembler/H. BC/4.18 supported one-pass assembly, multi-pass assembly, and stand-alone assembly, and was used to compile both high-level languages and assembly language programs.