Question

How to convert an int to scientific notation in C++

Answer 1

#include <iostream>
#include <string>
#include <cmath>

std::string toScientificManual(int n) {
    if (n == 0) return "0e+0";

    int exponent = 0;
    double mantissa = n;

    while (std::abs(mantissa) >= 10.0) {
        mantissa /= 10.0;
        exponent++;
    }
    while (std::abs(mantissa) < 1.0) {
        mantissa *= 10.0;
        exponent--;
    }

    char buffer[64];
    std::sprintf(buffer, "%.6fe%+d", mantissa, exponent);
    return buffer;
}


int main() {
    int x = 123456789;

    std::cout << toScientificManual(x);
}


/*
run:

1.234568e+8

*/

 

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Answer 2

#include <iostream>
#include <iomanip>

int main() {
    int x = 1234567891;

    std::cout << std::scientific << static_cast<double>(x) << "\n";
    
    std::cout << std::scientific << std::setprecision(3)
              << static_cast<double>(x) << "\n";
}



/*
run:

1.234568e+09
1.235e+09

*/

 

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