012_NumericStrings.cpp

// Coding Interviews: Questions, Analysis & Solutions
// Harry He

#include <stdio.h>

void scanDigits(char** string);
bool isExponential(char** string);

bool isNumeric(char* string)
{
    if(string == NULL)
        return false;

    if(*string == '+' || *string == '-')
        ++string;
    if(*string == '\0')
        return false;

    bool numeric = true;

    scanDigits(&string);
    if(*string != '\0')
    {
        // for floats
        if(*string == '.')
        {
            ++string;
            scanDigits(&string);
            
            if(*string == 'e' || *string == 'E')
                numeric = isExponential(&string);
        }
        // for integers
        else if(*string == 'e' || *string == 'E')
            numeric = isExponential(&string);
        else
            numeric = false;
    }

    return numeric && *string == '\0';
}

void scanDigits(char** string)
{
    while(**string != '\0' && **string >= '0' && **string <= '9')
        ++(*string);
}

bool isExponential(char** string)
{
    if(**string != 'e' && **string != 'E')
        return false;
        
    ++(*string);
    if(**string == '+' || **string == '-')
        ++(*string);

    if(**string == '\0')
        return false;

    scanDigits(string);
    return (**string == '\0') ? true : false;
}

// ==================== Test Code ====================

void Test(char* testName, char* string, bool expected)
{
    if(testName != NULL)
        printf("%s begins: ", testName);

    if(isNumeric(string) == expected)
        printf("Passed.\n");
    else
        printf("FAILED.\n");
}

int main(int argc, char* argv[])
{
    Test("Test1", "100", true);
    Test("Test2", "123.45e+6", true);
    Test("Test3", "+500", true);
    Test("Test4", "5e2", true);
    Test("Test5", "3.1416", true);
    Test("Test6", "600.", true);
    Test("Test7", "-.123", true);
    Test("Test8", "-1E-16", true);
    Test("Test9", "1.79769313486232E+308", true);

    printf("\n\n");

    Test("Test10", "12e", false);
    Test("Test11", "1a3.14", false);
    Test("Test12", "1+23", false);
    Test("Test13", "1.2.3", false);
    Test("Test14", "+-5", false);
    Test("Test15", "12e+5.4", false);

	return 0;
}