The first high-level programming language FORTRAN was published in 1954. In the following half century, over 500 high-level programming language have emerged, among which are some famous ones namely BASIC, Pascal, FoxPro, C and Java.

1.1 Key Items

1.1.1 Keywords

Keywords refer to a set of words that have special meaning within a programming language and are predefined in the language's formal specifications and that cannot be used as variables or procedure names. Keywords were also called reserved words before the widespread of C and Java language as was defined in the Java Language Specification (Gosling, 2011) and the ISO 9899 Standard for C Programming Language. 

Different languages have different keywords. For example, there are 36 reserved words in Pascal, as listed in Table 1.

Table 1 Keywords in Pascal

program function procedure array const file

label packed var record set type

case do down to else for goto

if of repeat then to until

while with forward and p in

mod not or nil begin end

Also, there are 32 keywords in C language, as listed in Table 2.

Table 2 Keywords in C

auto break case char const continue

default do double else enum exterm

float for goto if int long

register return short signed sizeof static

struct switch typeof union unsigned void

volatile while

Same language in different versions may have different keyword. The amount of keywords soars quickly to meet the addition of new functions, as listed in Table 3.

Table 3 Amount of Keywords文献综述

Language Name Amount of Keywords Objective Language Name Amount of Keywords

Basic