Thread: Integer manipulation

One way to reverse the digits of a number would be to count the digits in the number (1), then take each digit from the old number and put it into the right place in the new (2).

1. Counting the digits in a number.

Code:

for(temp = number; temp; temp /= 10, digits ++);

2a. Extracting a digit.

Code:

digit = number / pow(10, num) % 10;

2b. Assigning a digit.

Code:

newnumber = newnumber + digit * pow(10, newnum);

This should reverse an integer:

Code:

int reverse(int get){
    int temp=0,x;
    for(x=get;x!=0;x/=10){
        temp*=10;
        temp+=x%10;
    }
    return temp;
}

This has been asked before, quite recently.
Try a board search.

Oh, and this checks for overflow, if the number would be too big, it just outputs the highest (or lowest) possible value:

Code:

int reverse(int get){
    int temp=0,x;
    __int64 check=0;
    for(x=get;x!=0;x/=10){
        check*=10;
        check+=x%10;
        if(check>std::numeric_limits<int>::max() && get>0){
            return std::numeric_limits<int>::max();
        }
        else if(check*-1<std::numeric_limits<int>::min() && get<0){
            return std::numeric_limits<int>::min();
        }
        else{
            temp*=10;
            temp+=x%10;
        }
    }
    return temp;
}

You could always mention that __int64 is non-standard.

And std:: things don't work in C... sorry