1 Title Description
2 ideas and methods
(1) follows the pattern string representing the value A [[B].] [ E | EC] or [B]. [E | EC] , where A is the integer part of the value, B is the value of the fractional part after the decimal point, C followed by 'e' and 'E' is the value of exponent part. Note: There can be no number before the decimal point numbers.
The entire three-step process
A) the integer part of the value of the first scan; the first sign is first taken, the integer portion of the scan A
2) If you experience decimal point '.', Begins scanning fractional part B
3) If you have 'e' and 'E', directly under the portion C starts scanning
(2) Note that rule represents a numeric string to follow; may have a numerical value before the "+" or "-" followed by the digits 0 to 9 denotes the integer part of the value, if the value is a decimal, then after the decimal point there may be a plurality of digits 0 to 9, the value of the fractional part. If expressed in scientific notation, followed by an 'e' or 'E', and followed by an integer (which may have a sign) indicates the index.
3 C ++ core code
（1）
. 1 class Solution { 2 public : . 3 int index = 0 ; . 4 BOOL that isNumeric ( char * String ) . 5 { . 6 IF (! String ) return to false ; . 7 // digital format can be A [e | [[B] .] EC] or .B [e | EC], where a and C are 8 // integers (sign can have, or may not), and B is an unsigned integer . 9 BOOL In Flag scanInteger = ( String ); 10 IF (index <strlen ( String ) && String[index] == ' . ' ) { . 11 index ++ ; 12 is In Flag scanUnsignedInteger = ( String ) || In Flag; // . || reasons used here, the latter can not follow the foregoing figures. Note: This flag must be placed back ||! ! 13 is } 14 IF (index <strlen ( String ) && ( String [index] == ' E ' || String [index] == ' E ' )) { 15 index ++ ; 16 In Flag && scanInteger In Flag = ( String ); / /&& is used here reason, e | E must have a front of the back number . 17 } 18 is return In Flag == index && strlen ( String ); // NOTE: index == strlen (string) must be added !! counterexample 1a123 . 19 } 20 is BOOL scanInteger ( char * String ) { // scan + or - or empty initial digits 0-9, corresponding to a, C 21 is IF (index <strlen ( String ) && ( String [index] == ' + ' || String [index] == ' - ' )) 22 is index ++ ; 23 is returnscanUnsignedInteger ( String ); // to true indicates the presence of A or C 24 } 25 BOOL scanUnsignedInteger ( char * String ) { // scanning of digits 0-9, corresponding to B 26 is int Start = index; 27 the while (index <strlen ( String ) && String [index]> = ' 0 ' && String [index] <= ' . 9 ' ) 28 index ++ ; 29 return index> Start; // to true indicating the presence of B 30 } 31 32 };
（2）
1 // Note represents a numeric string to follow the rules; 2 // before value may have a "+" or "-" followed by the digits 0 to 9 denotes the integer part of the value, if the value is a decimal, then after the decimal point may have several digits 0 to 9 3 // fractional part of the value. If expressed in scientific notation, followed by an 'e' or 'E', and followed by an integer (which may have a sign) indicates the index. . 4 class Solution { . 5 public : . 6 BOOL that isNumeric ( char * String ) . 7 { . 8 IF ( String == NULL or * String == ' \ 0 ' ) . 9 return to false ; 10 IF (* String=='+'||*string=='-') 11 string++; 12 int dot=0,num=0,nume=0; 13 while(*string != '\0'){ 14 if(*string>='0' && *string<='9'){ 15 string++; 16 num =one ; 17 } 18 else if (* string == ' . ' ) { 19 if (dot> 0 || name> 0 ) 20 return false ; 21 string ++ ; 22 dot = 1 ; 23 } 24 else if (* string == ' e ' || * string == ' E ' ) { 25 if (name> 0 || num == 0 ) 26 return false ; 27 string ++ ; 28 name ++ ; 29 if (* string == ' + ' || * string == ' - ' ) 30 string ++ ; 31 if (* string == ' \ 0 ' ) 32 return false ; 33 } 34 else 35 return false; 36 } 37 return true; 38 } 39 };
Reference material
https://blog.csdn.net/fuqiuai/article/details/88198099
https://blog.csdn.net/u012477435/article/details/83351659#_873