No output from c++ loop

Question

Recently I coded a program to choose k numbers from the string in order from left to right to print out the number that has k characters and the smallest that can be made from the string itself for example : Input : 3 89678982 Output: 672 Then my code didn't print at all!! Code :

#include<bits/stdc++.h>
using namespace std;
int k,j=0,i;
string s;
int main() {
    cin>>k>>s;
    for(int i=0;i<s.size();i++) s[i]-=48;
    int the2=0;
    int Min=s[0];
    while(j<0) {
    for(i=the2;i<s.size();i++) {
            if(Min>s[i]) 
            {
                Min=s[i];
                break;
            }
        }
        the2=i;
        Min=s[i+1];
        cout<<Min;
        j++;
    }
}

Why did this happen and how do I fix it?

And what does your debugger say when you try to debug this code? — Evg, Jan 04 '22 at 12:24
You substracted '0' (48) from everything and now are printing control (invisible) characters. try std::cout << Min +'0'; — Pepijn Kramer, Jan 04 '22 at 12:27
Peoijn Kramer Min is an int and s[i] is a char. so if s[i]='7' (at the begenning) Min will be 7 It is not the best pactice but works. — Botond Horváth, Jan 04 '22 at 12:35
See [Why should I not #include ?](https://stackoverflow.com/q/31816095) and [Why using namespace std is bad practice](https://stackoverflow.com/questions/1452721). — prapin, Oct 16 '22 at 12:22

Vlad from Moscow · Answer 1 · 2022-01-04T13:12:38.700

For starters this condition of the while loop

while(j<0) {

evaluates to false at once because the variable j was initialized by 0.

int k,j=0,i;

Also this for loop

for(i=the2;i<s.size();i++) {
        if(Min>s[i]) 
        {
            Min=s[i];
            break;
        }
    }

finds the first character that is less than Min initially equal to the value s[0]. But you need to find the minimal value of the string in the range [0, s.length() - k + 1)

That is the program does do what is described in the assignment.

It seems you mean something like the following.

#include <iostream>
#include <string>
#include <iterator>
#include <algorithm>

int main()
{
    std::string s;
    size_t k = 0;

    std::cin >> k >> s;

    if (not ( s.size() < k ))
    {
        auto it = std::begin( s );

        for (size_t i = 0; i < k; i++)
        {
            it = std::min_element( it,
                     std::prev( std::end( s ), k - i - 1) );
            std::cout << *it++;
        }

        std::cout << '\n';
    }
}

If to enter

3 89678982

then the output will be

If to use a for loop instead of calling the standard algorithm std::min_element then program can look the following way

#include <iostream>
#include <string>
#include <iterator>
#include <algorithm>

int main()
{
    std::string s;
    size_t k = 0;

    std::cin >> k >> s;

    if (not ( s.size() < k ))
    {
        std::string::size_type pos = 0;

        for (size_t i = 0; i < k; i++)
        {
            for (auto j = pos; j < s.size() - k + i + 1; j++)
            {
                if (s[j] < s[pos]) pos = j;
            }

            std::cout << s[pos++];
        }

        std::cout << '\n';
    }
}

Thanks a lot! Also, can you explain to me why do I need to run the j loops to s.size()-k + 1 in order to find the minimum value? And also what does the size_t type mean? — Trương Quang Vinh, Jan 06 '22 at 00:08
@TrươngQuangVinh If k is equal for example 3 then the first digit may not be found in the last two characters of teh string because they are reserved for other two digits. size_t is unsigned integer type. — Vlad from Moscow, Jan 06 '22 at 08:18

score 1 · Answer 2 · answered Jan 04 '22 at 12:31

1

You don't print because j=0 so the while loop's condition (j<0) is false from the beginning. So it's body will not be executed at all. And your cout is inside that loop

answered Jan 04 '22 at 12:31

Botond Horváth

929
2
15

No output from c++ loop

2 Answers2