Program to check if a number belongs to a particular base or not

Difficulty Level : Medium
Last Updated : 12 Dec, 2017

Given a number N and its radix base R, find whether its valid or not according to its radix base.
Find valid/invalid number for any base ranging from binary to base32.
Examples:

Input : 1000101010001
Output : Valid
1000101010001 is valid binary number.

Input : 0xFFFAG
Output : invalid
0xFFFAG is not a valid hexa-decimal number because of character 'G' .

Method used : strspn

strspn :

strspn(numStr, validNumber)
Strspan: 
returns number of matching digits from 
character-set provided, so here it will return 1 - N,
where N is length of validNumber String.
numStr[]  : 
And that number is provided to numStr[] array.

numStr :

numStr[strspn(numStr, validNumber)]
Using this number as index for numStr[] array,
we access the digit there and it will be NULL 
in case string is matched and it will be non-zero 
if string is not matched

!numStr : And Finally we invert the result using invert operator to match for true case !
```
!numStr[strspn(numStr, validNumber)]
```

// Program to check if a number belongs 
// to particular base or not#include 
  
#include <cstdio> 
#include <cstdlib> 
#include <cstring> 
  
#define BINARY_BASE 2 // Defining binary base 
#define OCTAL_BASE 8 // Defining octal base 
#define DECIMAL_BASE 10 // Defining decimal base 
#define HEXA_BASE 16 // Defining hexa-decimal base 
#define BASE32_BASE 32 // Defining base32 base 
  
// Function prototypes 
bool isValid(const char* numStr, int base); 
const char* print(bool status); 
  
// Main method for base check 
int main(void) 
{ 
    // Defining valid/invalid numbers in radix bases 
    char* binaryStr = "1000101010001"; 
    char* decimalStr = "45221"; 
    char* base32Str = "AD22F"; 
  
    // invalid 
    char* octalStr = "7778A"; 
    char* hexStr = "FAG463"; 
  
    // Printing status of radix bases 
    printf("Binary string %s is %s\n", binaryStr, 
           print(isValid(binaryStr, BINARY_BASE))); 
    printf("Octal string %s is %s\n", octalStr, 
           print(isValid(hexStr, OCTAL_BASE))); 
    printf("Decimal string %s is %s\n", decimalStr, 
           print(isValid(decimalStr, DECIMAL_BASE))); 
    printf("Hex string %s is %s\n", hexStr, 
           print(isValid(hexStr, HEXA_BASE))); 
    printf("Base32 string %s is %s\n", base32Str, 
           print(isValid(base32Str, BASE32_BASE))); 
  
    return 0; 
} 
  
bool isValid(const char* numStr, int base) 
{ 
    // Defining valid base strings 
    const char* validBinary = "01"; 
    const char* validOctal = "01234567"; 
    const char* validDecimal = "0123456789"; 
    const char* validHex = "0123456789abcdefABCDEF"; 
    const char* validBase32 = "0123456789abcdefghijklmnopqrstuvABCDEFGHIJKLMNOPQRSTUV"; 
    const char* validNumber = NULL; 
  
    // Checking for valid base 
    validNumber = (base == BINARY_BASE) 
                      ? validBinary 
                      : ((base == OCTAL_BASE) 
                             ? validOctal 
                             : (base == DECIMAL_BASE) 
                                   ? validDecimal 
                                   : (base == HEXA_BASE) 
                                         ? validHex 
                                         : (base == BASE32_BASE) 
                                               ? validBase32 
                                               : NULL); 
  
    // Error checking for invalid base 
    if (validNumber == NULL) { 
        fputs("Invalid base encountered", stderr); 
        exit(EXIT_FAILURE); 
    } 
  
    // Check for valid base string usin strspn 
    return (!numStr[strspn(numStr, validNumber)]) ? true : false; 
} 
  
const char* print(bool status) 
{ 
    return (status) ? "Valid" : "Invalid"; 
} 

Output:

Binary string 1000101010001 is Valid
Octal string 7778A is Invalid
Decimal string 45221 is Valid
Hex string FAG463 is Invalid
Base32 string AD22F is Valid

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