D Documentation  
toString
char[] toString(bit arg)
char[] toString(char arg)
char[] toString(byte arg)
char[] toString(ubyte arg)
char[] toString(short arg)
char[] toString(ushort arg)
char[] toString(int arg)
char[] toString(uint arg)
char[] toString(long arg)
char[] toString(ulong arg)
char[] toString(float arg)
char[] toString(double arg)
char[] toString(real arg)
char[] toString(ifloat arg)
char[] toString(idouble arg)
char[] toString(ireal arg)
char[] toString(cfloat arg)
char[] toString(cdouble arg)
char[] toString(creal arg)

As you can see, the toString method really can convert integer and floating point numbers easily.
In addition you can define radix to convert an unsigned integer in a radix from 2 to 36:

char[] toString(long arg, uint radix);
char[] toString(ulong arg, uint radix);

Note: The characters A through Z are used to represent values 10 through 36.
Note: arg is treated as a signed value only if radix is 10!

Of course there is also a function to convert a C-style 0-terminated string s to char[.

char[] toString(char* s)
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