Question

How to count the number of digits in an integer with C++

Answer 1

#include <iostream>
#include <string>

int countDigitsString(int value) {
    // Convert the number to a string
    std::string text = std::to_string(value);

    // If negative, ignore the leading '-'
    if (!text.empty() && text[0] == '-') {
        return static_cast<int>(text.size()) - 1;
    }

    return static_cast<int>(text.size());
}

int main() {
    int number = -12345;

    int digits = countDigitsString(number);

    std::cout << "Number: " << number << "\n";
    std::cout << "Digit count (String method): " << digits << "\n";
}



/*
run:

Number: -12345
Digit count (String method): 5

*/

 

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Answer 2

#include <iostream>
#include <cmath>

int countDigitsLog10(int value) {
    int num = std::abs(value);

    // Zero must be handled explicitly
    if (num == 0) {
        return 1;
    }

    // Use floor(log10(n)) + 1
    return static_cast<int>(std::floor(std::log10(num))) + 1;
}

int main() {
    int number = 987654321;

    int digits = countDigitsLog10(number);

    std::cout << "Number: " << number << "\n";
    std::cout << "Digit count (log10 method): " << digits << "\n";
}



/*
run:

Number: 987654321
Digit count (log10 method): 9

*/

 

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