将整数放入数组C ++

Question

this is a super simple problem but it's late and I cant figure out for the life of me why this function doesnt work. I want it to print 1234, but instead it prints 123121. can someone explain what's going on and how to fix it? thanks

#include <iostream>

const int size = 20;

void set_int( int num )
{
    int digits[size];
    for ( int i = size - 1; i >= 0; i-- )
    {
        digits[i] = num % 10;
        num /= 10;
        if ( num != 0 )
            std::cout << num;
    }
}

int main()
{
    set_int( 1234 );
    return 0;
}

Answer 1

Well you are outputting the number instead of the digit .

Try changing like,

cout << digits[i] 

Further clarification :

On the first run of the loop your num will be 1234 / 10 = 123

Next run your number will be 123 / 10 = 12

Next is going to be 1

You are outputing num, so you get 123121 .

Answer 2

There are several things wrong with that code.

Firstly, the definition

int digits[size];

is a variable length array, which is valid C (since the 1999 C standard) but is not valid C++. Unfortunately, some C++ compilers support such things as an extension.

Second, even if we assume that definition is valid, your code is essentially stating that you need an array with 1234 elements to hold integral values corresponding to four digits (1,2,3, and 4).

As MichaelCMS has described, your code is outputting something other than the digits too. A value of 1234 has 4 digits, so you would need to loop a total of 4 times to find all digits (if doing it right). You would not need to loop 1234 times.

Answer 3

MichaelCMS explained correctly, why you have such output. There are mistakes in your function. I wrote another one.

You can use next code, which helps to find digits of number.

#include <iostream>

int FindNumberOfDigits(int number);
void SplitNumberIntoDigits(int number);  

// Splits number into digits. 
// Works with not big numbers.
void SplitNumberIntoDigits(int number)
{
    int size = FindNumberOfDigits(number);      

    int * digits = new int[size];

    int divider = 0;
    int degree = 0;     

    for(int digit = size; digit > 0; digit --)
    {
        // Find degree of divider
        degree = digit; 

        // Find divider for each digit of number.
        // For 1234 it will be 1000. For 234 it will be 100.            
        divider = pow(10, degree - 1);

        // We use "abs" to get digits without "-".
        // For example, when -1234 / 1000, you get -1.
        digits[digit] = abs(number / divider);  

        // Cut number to find remaining digits.
        number %= divider;                      
        std::cout << digits[digit];
    }   

    std::cout << std::endl; 
}

// If number = 0, number of digits will be 1.
// Else returns number of digits.   
int FindNumberOfDigits(int number)
{
    int digitsNumber = 0;   

    if (number)
    {
        // calculates number of digits
        while (number / 10)
        {
            number /= 10;
            digitsNumber ++;
        }                  
    }

    digitsNumber += 1;          

    return digitsNumber;        
}


int _tmain(int argc, _TCHAR* argv[])
{   
    SplitNumberIntoDigits(1234);
    SplitNumberIntoDigits(0);
    SplitNumberIntoDigits(1);
    SplitNumberIntoDigits(-1234);
    SplitNumberIntoDigits(1234567890);  

    return 0;
}

As a result this code can help you to find digits of not big numbers. It works with positive, negative numbers and zero.