convert 180F to C
convert 180C to F
convert 30" to cm
etc

checking key: (?i-xsm:(\d+)C)
Matched C with 180
convert 180F to C
convert 356F to F
convert 30" to cm
etc

checking key: (?i-xsm:(\d+)F)
Matched F with 180
Matched F with 356
convert 82C to C
convert 180C to F
convert 30" to cm
etc

convert 82C to C
convert 180C to F
convert 30" to cm
etc