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  1. #include <iostream>
  2. #include <iomanip>
  3. #include <cmath>
  4.  
  5. using namespace std;
  6.  
  7. class Double
  8. {
  9. public:
  10.     Double(const char * s);
  11.  
  12.     operator double() const { return sign*v*pow(10,ex*exsn); }
  13. private:
  14.  
  15.     int start(char c);
  16.     int zero (char c);
  17.     int one  (char c);
  18.     int two  (char c);
  19.     int three(char c);
  20.     int four (char c);
  21.     int five (char c);
  22.  
  23.     double v  =  0;
  24.     int sign  =  1;
  25.     int ex    =  0;
  26.     int exsn  =  1;
  27.     int state = -1;
  28.     double p  = 10;
  29. };
  30.  
  31. Double::Double(const char * s)
  32. {
  33.     if ((state = start(*s++)) < 0) return;
  34.     for(;*s;++s)
  35.     {
  36.         switch(state)
  37.         {
  38.         case 0: state = zero (*s); break;
  39.         case 1: state = one  (*s); break;
  40.         case 2: state = two  (*s); break;
  41.         case 3: state = three(*s); break;
  42.         case 4: state = four (*s); break;
  43.         case 5: state = five (*s); break;
  44.         default: return;
  45.         }
  46.     }
  47. }
  48.  
  49. int Double::start(char c)
  50. {
  51.     if (c == '-' || c == '+') { sign = (c == '-') ? -1 : 1; return 0; }
  52.     if (c == '.') return 2;
  53.     if (isdigit(c)) { v = v*10 + (c-'0'); return 1; }
  54.     return -1;
  55. }
  56.  
  57. int Double::zero(char c)
  58. {
  59.     if (c == '.') return 2;
  60.     if (isdigit(c)) { v = v*10 + (c-'0'); return 1; }
  61.     return -1;
  62. }
  63.  
  64. int Double::one(char c)
  65. {
  66.     if (c == '.') return 2;
  67.     if (c == 'e' || c == 'E') return 4;
  68.     if (isdigit(c)) { v = v*10 + (c-'0'); return 1; }
  69.     return -1;
  70. }
  71.  
  72. int Double::two(char c)
  73. {
  74.     if (isdigit(c)) { v = v + (c-'0')/p; p*=10; return 3; }
  75.     return -1;
  76. }
  77.  
  78. int Double::three(char c)
  79. {
  80.     if (isdigit(c)) { v = v + (c-'0')/p; p*=10; return 3; }
  81.     if (c == 'e' || c == 'E') return 4;
  82.     return -1;
  83. }
  84.  
  85. int Double::four(char c)
  86. {
  87.     if (c == '-' || c == '+') { exsn = (c == '-') ? -1 : 1; return 5; }
  88.     if (isdigit(c)) { ex = ex*10 + (c-'0'); return 5; }
  89.     return -1;
  90. }
  91.  
  92. int Double::five(char c)
  93. {
  94.     if (isdigit(c)) { ex = ex*10 + (c-'0'); return 5; }
  95.     return -1;
  96. }
  97.  
  98. int main(int argc, char * argv[])
  99. {
  100.     string s;
  101.     while(cin >> s)
  102.     {
  103.         cout << setw(15) << s << "  " << setprecision(25) << Double(s.c_str()) << endl;
  104.     }
  105. }
  106.  
Success #stdin #stdout 0.01s 5528KB
comments (?)
stdin
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3.14151926
0.256E18
-.123e45
1.2a763527
+.456tt7862
stdout
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     3.14151926  3.141519260000000368648898
       0.256E18  256000000000000000
       -.123e45  -1.23000000000000001342895e+44
     1.2a763527  1.199999999999999955591079
    +.456tt7862  0.4560000000000000164313008
https://ideone.com/BQGaFw
language:
C++14 (gcc 8.3)
created:
3 years ago
visibility:
secret

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