Finding the Largest Digit in C++ [duplicate] - c++

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How do I extract the digits of a number in C++?
(6 answers)
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Input a 3-digit integer.
Print the largest digit in the integer (Tip: use % 10 to get the rightmost digit, and / 10 to remove the rightmost digit).
Input: 173
Expected Output: 7
We were given this activity 2 days old and still couldn't solve this mystery. Here's my own code which doesn't match the given expected output above:
#include<iostream>
using namespace std;
int main() {
int num, result;
cin >> num;
if(num > 0) {
result = num % 10;
num / 10;
cout << result;
}
return 0;
}

Answer 1

You separate only the last digit, but need to check all - just add a loop. Also num / 10 does nothing.
maxdigit = 0;
while (num > 0) {
maxdigit = max(maxdigit, num % 10);
num /= 10;
}
cout << maxdigit;

Answer 2

Different way to solve the problem. Take the input as a string. You can handle much larger numbers and the string is already decomposed into digits. You barely have to think. Just work through the string character-by-character, make sure the character is a digit, and keep track of the biggest digit seen so far.
#include<iostream>
#include <cctype> // needed for isdigit
//using namespace std; Not recommended. Causes problems
int main()
{
std::string num;
char max = 0;
std::cin >> num; // read number as a string.
for (char ch: num)
{ //iterate string character by character
if (!isdigit(static_cast<unsigned char>(ch)))
{ // if we didn't get a digit, the user screwed up (or is a jerk)
// Let's not assume malice and let them know they've made a mistake.
std::cerr << "Must input a valid number";
return -1;
}
if (ch > max)
{ // this is the biggest character seen so far.
max = ch; // update biggest
}
}
std::cout << max; // print biggest
return 0;
}

Answer 3

The answer of MBo is the best and should be accepted.
You are obviously not allowed to use C++ algorithms yet. And, maybe you are learing now about interger and modulo divisions.
If you would be allowed to use more advanced C++, you would probably write something like:
#include <iostream>
#include <algorithm>
int main()
{
if (std::string number{}; (std::cin >> number) and std::all_of(number.begin(), number.end(), ::isdigit))
std::cout << *max_element(number.begin(), number.end()) << '\n';
}

Answer 4

Below is the working example without using loops and without using std::max. Note this(without loop) is just one among many possible ways of doing it.
#include <iostream>
int findDigit(int passed_num, int current_num)
{
int lastDigit;
if (passed_num == 0) {
return current_num;
}
// find the last didit
lastDigit = passed_num % 10;
if(lastDigit > current_num)
{
current_num = lastDigit;
}
//call findDigit() repeatedly
current_num = findDigit(passed_num / 10, current_num);
std::cout<<lastDigit<<" ";
return current_num;
}
int main()
{
std::cout << "Enter a number: ";
int input_num, greatest_num;
std::cin>>input_num;
greatest_num = findDigit(input_num, 0);
std::cout<<"greatest is: "<<greatest_num<<std::endl;
std::cout<<"Enter another number: ";
std::cin>>input_num;
greatest_num = findDigit(input_num, 0);
std::cout<<"greatest is: "<<greatest_num<<std::endl;
return 0;
}
The output of the above is as follows:
Enter a number: 24344357
2 4 3 4 4 3 5 7 greatest is: 7
Enter another number: 2353639
2 3 5 3 6 3 9 greatest is: 9

Answer 5

#include <iostream>
using namespace std;
int main() {
int a = 11;
int b = 5;
int c = 23;
int max = (a>b) ? ((a>c) ? a : c) : ((b>c) ? b : c) ;
cout << max << endl;
}//using Ternary Operator