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built-in functions
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This subchapter looks at built-in functions.
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This subchapter looks at built-in functions.
free computer programming text book projecttable of contents
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This subchapter is a stub section. It will be filled in with instructional material later. For now it serves the purpose of a place holder for the order of instruction.
Professors are invited to give feedback on both the proposed contents and the propsed order of this text book. Send commentary to Milo, PO Box 1361, Tustin, California, 92781, USA.
This subchapter looks at built-in functions.
Built-in functions provide a wide variety of useful capabilities. While this chapter is about calculations and most programming languages have a rich set of built-in functions for calculations, built-in functions have much wider uses.
Most programming languages invoke a built-in function by giving the name of the built-in function followed by any input. The inputs are usually placed inside parenthesis, but this varies by language. Most languages treat the output of a built-in function in much the same manner as fetching the value of a variable and typically a built-in function can be placed anywhere in an expression that a variable of the same kind could be placed. The results of the built-in function usually can be used in assignments and computations.
The form would typically look something like:
a := abs(b);
In the example, the built-in function takes the value of the variable a, finds its absolute value, and then assigns the answer to the variable b.
The following discussion of JOVIAL (an old programming language) gives the flavor of the kinds of uses for built-in functions.
The following material is from the unclassified Computer Programming Manual for the JOVIAL (J73) Language, RADC-TR-81-143, Final Technical Report of June 1981.
1.1.5 Built-In Functions
The JOVIAL built-in functions provide advanced, specialized
operations that are not covered by the JOVIAL operators. They
are summarized in the following table:
Function result
LOC(x) A pointer to the object referenced by r
NEXT(p,i) A pointer to the i'th data object after
the one selected by p
NEXT(s,i) The i'th status value after status value s
BIT(b,i,n) A string of n bits starting at the i'th bit
of the bit string b
BYTE(c,i,n) A string of n characters starting at the i'th
character of the character string c
SHIFTL(b,n) Bit string b shifted left by n bits
SHIFTR(b,n) Bit string b shifted right by n bits
ABS(x) Absolute value of x
SGN(x) +1, 0, or -1 for x>0, x=0, x<0
BITSIZE(x) Logical size of x in bits
BYTESIZE(x) Logical size of x in bytes
WORDSIZE(x) Logical size of x in words
LBOUND(t,d) Lower bound of d'th dimension of the table t
UBOUND(t,d) Upper bound of d'th dimension of the table t
NWSDEN(t) Number of bytes allocated to each entry of
the table t
FIRST(s) First status value in status list for s
LAST(s) Last status value in status list for s
An example of the use of a built-in function is:
C = BYTE("ABCDEF",2,3);
The built-in functions extracts "BCD" from the string "ABCDEF".
Chapter 1 Introduction, page 9
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