How do i take user input of an Arithmetic Expression like 5-8+7*4-8+9 or 1+5?

I am solving a problem for finding maximum value of an arithmetic expression. But I am having problem in taking input for the expression as no of characters are not fixed.

Input Format:

• The only line of the input contains a string s of length 2n + 1 for some n, with symbols s0 , s1 , . . . , s2n.
• Each symbol at an even position of s is a digit (that is, an integer from 0 to 9)
• while each symbol at an odd position is one of three operations from {+,-,*}.

But I want digits and symbols in different arrays(digits in an int array and operations in a char array) for my solution.

This is how I implemented originally:

  string s;
  std::cin >> s;

  n=s.size();
  cout<<"n= "<<n<<endl;

  vector<long long> no;
  vector<char> ops;

  for(int i = 0; i <n; i++)
  {
    if(i%2==0)
    {
      no.push_back(s[i]);
    }
    else{
      ops.push_back(s[i]);
    }
  }

But I am not being able to get required input, instead getting this:

INPUT:
5-8+7*4-8+9

OUTPUT:
n = 11
no[0] = 53
no[1] = 56
no[2] = 55
no[3] = 52
no[4] = 56
no[5] = 57
ops[0] = -
ops[1] = +
ops[2] = *
ops[3] = -
ops[4] = +

I have also tried one more solution:

  vector<long long> no;
  vector<char> ops;

  int i=0;
  while(cin)
  {

    cout<<"i= "<<i<<endl;
    if(i%2==0)
    {
      int s;
      cin>>s;
      if(s=='\0')
      {
        exit();
      }
      cout<<"s= "<<s<<endl;
      no.push_back((int)s);
      cout<<"no= "<<no[i/2]<<endl;
    }
    else
    {
      char s;
      cin>>s;
      if(s=='\0')
      {
        exit();
      }
      cout<<"s= "<<s<<endl;
      ops.push_back(s);
      cout<<"ops= "<<ops[(i-1)/2]<<endl;
    }
    i++;
  }

But this goes into infinite loop.

Please help me out

Your output seems to be correct, but as already mentioned in the comments, your values are read as characters, not as digits, so a conversion needs to be done.

In order to do this, it might be helpful to understand that, in ASCII, the digits have following value:

Character ASCII-code value
      '0'         48     0
      '1'         49     1
      '2'         50     2
      '3'         51     3
      '4'         52     4
      '5'         53     5
      '6'         54     6
      '7'         55     7
      '8'         56     8
      '9'         57     9

How to get the value out of the character value? Easy :

value(<character>) = ASCII_code(<character>) - ASCII_code('0'), or:
                   = ASCII_code(<character>) - 48