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B語言是一種通用的程式語言。自從被C語言取代之後，幾乎已遭棄置。
B語言大約是於1969年時由美國貝爾實驗室的電腦科學家──肯·湯普森在丹尼斯·利奇的支持下設計出來的。肯·湯普森最初想在UNIX上開發一個Fortran編譯器，但後來引進了BCPL的風格，形成一個新的語言。
後來，丹尼斯·利奇以B語言為基礎開發出C語言，至此C語言漸漸發展成為目前世界上最常用的程式語言之一。
下面是肯·湯普森在《B用戶參考》中提供的源代碼[2]：
/* The following function will print a non-negative number, n, to
the base b, where 2<=b<=10. This routine uses the fact that
in the ASCII character set, the digits 0 to 9 have sequential
code values. */
printn(n, b) {
extrn putchar;
auto a;
/* Wikipedia note: auto declares a variable with automatic
storage (lifetime is function scope), not "automatic typing"
as in C++11. */
if (a = n / b) /* assignment, not test for equality */
printn(a, b); /* recursive */
putchar(n % b + '0');
}
/* The following program will calculate the constant e-2 to about
4000 decimal digits, and print it 50 characters to the line in
groups of 5 characters. The method is simple output conversion
of the expansion
1/2! + 1/3! + ... = .111....
where the bases of the digits are 2, 3, 4, . . . */
main() {
extrn putchar, n, v;
auto i, c, col, a;
i = col = 0;
while(i<n)
v[i++] = 1;
while(col<2*n) {
a = n+1 ;
c = i = 0;
while (i<n) {
c =+ v[i] *10;
v[i++] = c%a;
c =/ a--;
}
putchar(c+'0');
if(!(++col%5))
putchar(col%50?' ': '*n');
}
putchar('*n*n');
}
v[2000];
n 2000;
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