C99:

• input: 2.5+6.75I
• output: 2.50+6.75I

Fortran:

• input: (2.5,6.75)
• output with decimal point: (2.50, 6.75) or 2.50+I6.75
• output with decimal comma: (2,50; 6,75) or 2,50+I6,75

Haskell:

• input: 2.5 :+ 6.75
• output: 2.5 :+ 6.75

Lisp:

• input: c#(2.5 6.75)
• output: C#(2.5 6.75)

Lua:

• input: {2.5, 6.75} or complex "2.5+6.75i"
• output: 2.5+6.75i

Perl:

• input: cplx(2.5, 6.75)
• output: 2.5+6.75i

Python:

• input: c{2.5, 6.75}
• output: (2.5+6.75j)

Ruby:

• input: Complex(2.5, 6.75)
• output: Complex(2.5, 6.75)