ctrl key其实是用于扩展键盘，单独一个ctrl键没有什么作用，也没有ascii码，当与其他键相结合时，相当于创造出一个新键。例如：用getchar()侦测输入的字符，当按下ctrl+a时，只输出了一个ascii码1。只按下ctrl键没有输出。因此ctrl+a其实只相当于一个键罢了。
下表为所有的ctrl组合键的ascii码及其名字。
| Control | Code | To Enter With | Echo | ||||||
| Abbreviation | Full Name | Dec | Hex | Alt-Key | Ctrl-Key | ||||
| NUL | Null | 0 | 00 | Ctrl-@ | ^@ | ||||
| SOH | Start of heading | 1 | 01 | Alt-1 | Ctrl-A | ^A | |||
| STX | Start of text | 2 | 02 | Alt-2 | Ctrl-B | ^B | |||
| ETX | End of text | 3 | 03 | Alt-3 | Ctrl-C | ^C | |||
| EOT | End of transmission | 4 | 04 | Alt-4 | Ctrl-D | ^D | |||
| ENQ | Enquiry | 5 | 05 | Alt-5 | Ctrl-E | ^E | |||
| ACK | Acknowledge | 6 | 06 | Alt-6 | Ctrl-F | ^F | |||
| BEL | Bell | 7 | 07 | Alt-7 | Ctrl-G | ^G | |||
| BS | Backspace | 8 | 08 | Alt-8 | Ctrl-H | ^H | |||
| HT | Horizontal tab | 9 | 09 | Alt-9 | Ctrl-I | ^I | |||
| LF | Line feed | 10 | 0A | Alt-10 | Ctrl-J | ^J | |||
| VT | Vertical tab | 11 | 0B | Alt-11 | Ctrl-K | ^K | |||
| FF | Form feed | 12 | 0C | Alt-12 | Ctrl-L | ^L | |||
| CR | Carriage return | 13 | 0D | Alt-13 | Ctrl-M | ^M | |||
| SO | Shift out | 14 | 0E | Alt-14 | Ctrl-N | ^N | |||
| SI | Shift in | 15 | 0F | Alt-15 | Ctrl-O | ^O | |||
| DLE | Data line escape | 16 | 10 | Alt-16 | Ctrl-P | ^P | |||
| DC1 | Device control 1 | 17 | 11 | Alt-17 | Ctrl-Q | ^Q | |||
| DC2 | Device control 2 | 18 | 12 | Alt-18 | Ctrl-R | ^R | |||
| DC3 | Device control 3 | 19 | 13 | Alt-19 | Ctrl-S | ^S | |||
| DC4 | Device control 4 | 20 | 14 | Alt-20 | Ctrl-T | ^T | |||
| NAK | Negative acknowledge | 21 | 15 | Alt-21 | Ctrl-U | ^U | |||
| SYN | Synchronous idle | 22 | 16 | Alt-22 | Ctrl-V | ^V | |||
| ETB | End transmission block | 23 | 17 | Alt-23 | Ctrl-W | ^W | |||
| CAN | Cancel | 24 | 18 | Alt-24 | Ctrl-X | ^X | |||
| EM | End of medium | 25 | 19 | Alt-25 | Ctrl-Y | ^Y | |||
| SUB | Substitute | 26 | 1A | Alt-26 | Ctrl-Z | ^Z | |||
| ESC | Escape | 27 | 1B | Alt-27 | Ctrl-[ | ^[ | |||
| FS | File separator | 28 | 1C | Alt-28 | Ctrl-\ | ^\ | |||
| GS | Group separator | 29 | 1D | Alt-29 | Ctrl-] | ^] | |||
| RS | Record separator | 30 | 1E | Alt-30 | Ctrl-^ | ^^ | |||
| US | Unit separator | 31 | 1F | Alt-31 | Ctrl-_ | ^_ | |||