If your compiler does not provide overloaded functions for integral types (it isn't required to), you'll have to explicitly cast to another type, namely one of these three:
That's not the problem, the problem is that for some reason the sqrt() (and sin() and cos()) functions don't seem to be defined. The funny thing is, I've used sqrt() before and it worked.
c:\program files\microsoft visual studio 9.0\vc\include\cmath(21) : error C2039: 'acosf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(21) : error C2873: 'acosf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(21) : error C2039: 'asinf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(21) : error C2873: 'asinf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(22) : error C2039: 'atanf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(22) : error C2873: 'atanf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(22) : error C2039: 'atan2f' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(22) : error C2873: 'atan2f' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(22) : error C2039: 'ceilf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(22) : error C2873: 'ceilf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(23) : error C2039: 'cosf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(23) : error C2873: 'cosf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(23) : error C2039: 'coshf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(23) : error C2873: 'coshf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(23) : error C2039: 'expf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(23) : error C2873: 'expf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(24) : error C2039: 'fabsf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(24) : error C2873: 'fabsf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(24) : error C2039: 'floorf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(24) : error C2873: 'floorf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(24) : error C2039: 'fmodf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(24) : error C2873: 'fmodf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(25) : error C2039: 'frexpf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(25) : error C2873: 'frexpf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(25) : error C2039: 'ldexpf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(25) : error C2873: 'ldexpf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(25) : error C2039: 'logf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(25) : error C2873: 'logf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(26) : error C2039: 'log10f' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(26) : error C2873: 'log10f' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(26) : error C2039: 'modff' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(26) : error C2873: 'modff' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(26) : error C2039: 'powf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(26) : error C2873: 'powf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(27) : error C2039: 'sinf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(27) : error C2873: 'sinf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(27) : error C2039: 'sinhf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(27) : error C2873: 'sinhf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(27) : error C2039: 'sqrtf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(27) : error C2873: 'sqrtf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(28) : error C2039: 'tanf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(28) : error C2873: 'tanf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(28) : error C2039: 'tanhf' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(28) : error C2873: 'tanhf' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(30) : error C2039: 'acosl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(30) : error C2873: 'acosl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(30) : error C2039: 'asinl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(30) : error C2873: 'asinl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(31) : error C2039: 'atanl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(31) : error C2873: 'atanl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(31) : error C2039: 'atan2l' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(31) : error C2873: 'atan2l' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(31) : error C2039: 'ceill' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(31) : error C2873: 'ceill' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(32) : error C2039: 'cosl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(32) : error C2873: 'cosl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(32) : error C2039: 'coshl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(32) : error C2873: 'coshl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(32) : error C2039: 'expl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(32) : error C2873: 'expl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(33) : error C2039: 'fabsl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(33) : error C2873: 'fabsl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(33) : error C2039: 'floorl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(33) : error C2873: 'floorl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(33) : error C2039: 'fmodl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(33) : error C2873: 'fmodl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(34) : error C2039: 'frexpl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(34) : error C2873: 'frexpl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(34) : error C2039: 'ldexpl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(34) : error C2873: 'ldexpl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(34) : error C2039: 'logl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(34) : error C2873: 'logl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(35) : error C2039: 'log10l' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(35) : error C2873: 'log10l' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(35) : error C2039: 'modfl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(35) : error C2873: 'modfl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(35) : error C2039: 'powl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(35) : error C2873: 'powl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(36) : error C2039: 'sinl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(36) : error C2873: 'sinl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(36) : error C2039: 'sinhl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(36) : error C2873: 'sinhl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(36) : error C2039: 'sqrtl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(36) : error C2873: 'sqrtl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(37) : error C2039: 'tanl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(37) : error C2873: 'tanl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(37) : error C2039: 'tanhl' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(37) : error C2873: 'tanhl' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(41) : error C2039: 'acos' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(41) : error C2873: 'acos' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(41) : error C2039: 'asin' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(41) : error C2873: 'asin' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(42) : error C2039: 'atan' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(42) : error C2873: 'atan' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(42) : error C2039: 'atan2' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(42) : error C2873: 'atan2' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(42) : error C2039: 'ceil' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(42) : error C2873: 'ceil' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(43) : error C2039: 'cos' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(43) : error C2873: 'cos' : symbol cannot be used in a using-declaration
c:\program files\microsoft visual studio 9.0\vc\include\cmath(43) : error C2039: 'cosh' : is not a member of '`global namespace''
c:\program files\microsoft visual studio 9.0\vc\include\cmath(43) : fatal error C1003: error count exceeds 100; stopping compilation