====== dc ======
Reverse-Polish calculator and one of the oldest Unix utilities.

===== Commands =====
^ ^ Command ^ Use ^
^ Printing |
^ | p | print the stack top without altering the stack |
^ | n | pops the stack top and prints it without a newline |
^ | P | pops the stack top; if a string, print it without a newline; otherwise print the integer value as a byte stream |
^ | f | print the entire stack top to bottom without altering anything |
^ Arithmetic | 
| | + | pops two values, adds them, and pushes the result |
| | - | pops two values, subtracts the first popped from the second, and pushes the result |
| | * | pops two values, multiplies them, and pushes the result |
| | / | pops two values, divides the second popped by the first, and pushes the result |
| | % | pops two values, calculates the remainder of the division that / would perform, and pushes that |
| | ~ | pops two values, divides the second popped by the first popped, then pushes the quotient followed by the remainder |
| | \^ | pops two values, raises the second popped to the power of the first popped, and pushes the result |
| | \| | pops three values; the first popped is a reduction modulus, the third is the base, and the second is the exponent |
| | v | pops one value and computes its square root |
^ Stack control |
| | c | clears the stack |
| | d | duplicates the value on top of the stack |
| | r | swaps the top two values on the stack |
| | R | pops the top value as an integer $n$, then rotates the top $n$ elements of the stack; if the stack has fewer than $n$ elements, the entire stack is rotated |
^ Registers |
| | s__r__ | pop the stack top and store it in register __r__ |
| | l__r__ | copy the value from register __r__ and push it to the stack |
| | S__r__ | pop the top of the main stack and push it onto the stack of register __r__ |
| | L__r__ | pop the top of register __r__'s stack and push it onto the main stack |
^ Parameters |
| | i | pops a value off the stack and uses it as the input radix |
| | o | pops a value off the stack and uses it as the output radix |
| | k | pops a value off the stack and uses it to set the precision |
| | I | pushes the current input radix onto the stack |
| | O | pushes the current output radix onto the stack |
| | K | pushes the current precision onto the stack |
^ Strings |
| | [__text__] | pushes __text__ to the stack as a string |
| | a | pops the top of stack; if it was a number, the low-order byte is converted to a string and pushed onto the stack; otherwise, the first character of the string is pushed back |
| | x | pops a value off the stack and executes it as a macro; if the stack top was a number, it is simply pushed back |
| | >__r__ | pops two values and compares them as numbers, then executes the contents of __r__ as a macro if the first popped is greater than the second |
| | !>__r__ | similar, but invokes the macro if the first popped is not greater than the second |
| | <__r__ | similar, but invokes the macro if the first popped is less than the second |
| | !<__r__ | similar, but invokes the macro if the first popped is not less than the second |
| | =__r__ | similar, but invokes the macro if the two numbers are equal |
| | !=__r__ | similar, but invokes the macro if the two numbers are not equal |
| | ? | reads a line from the terminal and executes it, allowing for user input |
| | q | exits from a macro and from the macro which invoked it; if called from the top level, exits dc |
| | Q | pops a value off the stack and uses it as a count of macro levels to exit; will never cause dc to exit |
^ Status inquiry |
| | Z | pops a value off the stack, calculates the number of decimal digits (or number of characters if a string) it has, and pushes that number; this does not include any leading zeros |
| | X | pops a value off the stack, calculates the number of fraction digits it has, and pushes that number; if a string, the value pushed is 0 |
| | z | pushes the current stack depth |
^ Miscellaneous |
| | ! | executes the rest of the line as a system command; if the command begins with <, =, or >, then a space must be present after the ! |
| | # | interprets the rest of the line as a comment |
| | :__r__ | pops the top two values off the stack, storing the second popped in the array __r__, indexed by the first popped |
| | ;__r__ | pops the top of stack and uses it as an index into array __r__; the selected value is then pushed onto the stack |

===== Samples =====
<WRAP center round todo 60%>
Break these examples out with comments
</WRAP>

  * sum the entire stack: ''0d[+z1<a]dsaxp''
  * calculate the GCD of the top two stack values: ''[dSarLa%d0<a]dsax+p''
  * compute the factorial of the stack top: ''[q]sQ[d1=Qd1-lFx*]dsFxp''

===== Resources =====
  * [[man>dc|man page]]

{{tag>cli}}