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  1. #include <cassert>
  2. #include <cctype>
  3.  
  4. // true if positive or negative number including decimal points
  5. //   42
  6. //   42.56
  7. //  +42
  8. //  -42
  9. // false otherwise
  10. //   42. --> false
  11. //  ++42
  12. //  +.
  13. //  4+
  14. //  regexp := [+|-][d+][.][d+]
  15. //   start -> sign -> digit -> decimal -> digit
  16. //   reject 
  17. bool isnumeric( char const * );
  18.  
  19. bool
  20. isnumeric( char const * str ) {
  21.  
  22.   if( !str ) { return false; }
  23.  
  24.   int signs = 0;
  25.   int decimals = 0;
  26.   int digits = 0;
  27.   int digitsAfterDecimal = 0;
  28.  
  29.   for( char const * p = str; *p; ++p ) {
  30.  
  31.     if( (*p == '+') || (*p == '-') ) {
  32.       if( (decimals > 0) || (digits > 0) ) {
  33.         return false;
  34.       }
  35.       signs += 1;
  36.       if( signs == 2 ) {
  37.         return false;
  38.       }
  39.     }
  40.     else if( *p == '.' ) {
  41.       decimals += 1;
  42.       if( decimals == 2 ) {
  43.         return false;
  44.       }
  45.     }
  46.     else if( ! isdigit( *p ) ) {
  47.       return false;
  48.     }
  49.     else {
  50.       digits += 1;
  51.       if( decimals > 0 ) {
  52.         digitsAfterDecimal += 1;
  53.       }
  54.     }
  55.   }
  56.  
  57.   return (decimals > 0) ? ((digits > 0) && (digitsAfterDecimal > 0))
  58.                         : (digits > 0) ;
  59. }
  60.  
  61. void test_isnumeric() {
  62.   assert( isnumeric( "42" ) );
  63.   assert( isnumeric( "42.0" ) );
  64.   assert( isnumeric( "42.56" ) );
  65.   assert( isnumeric( "+42" ) );
  66.   assert( isnumeric( ".42" ) );
  67.   assert( isnumeric( "+.42" ) );
  68.  
  69.   assert( ! isnumeric( "42." ) );
  70.   assert( ! isnumeric( "++42" ) );
  71.   assert( ! isnumeric( "+." ) );
  72.   assert( ! isnumeric( "4+" ) );
  73. }
  74.  
  75. int main( void ) {
  76.   test_isnumeric();
  77. }
  78.  
Success #stdin #stdout 0s 3336KB
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https://ideone.com/qotAhb
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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