Yukicoder緑<No.42B>

問題

問題はこちら
問題文↓

'+'は掛け算を表す演算子、'*'は足し算を表す演算子です
式が与えられるので、左から順番にこの計算をしてください

解法

演算子の定義を間違えずに、左から順番に見ていく
演算子が来たら、前の演算子を計算して、保存を繰り返す

#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (ll i = 0; i < (n); ++i)
#define rep1(i, n) for (ll i = 1; i < (n); ++i)
#define rrep(i, n) for (ll i = n; i > 0; --i)
#define bitrep(i, n) for (ll i = 0; i < (1 << n); ++i)
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define yesNo(b) ((b) ? "Yes" : "No")
using ll = long long;
using ull = unsigned long long;
using ld = long double;
string alphabet = "abcdefghijklmnopqrstuvwxyz";
string ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const double pi = 3.141592653589793;
int smallMOD = 998244353;
int bigMOD = 1000000007;

int main()
{
    string s;
    cin >> s;
    string num1 = "";
    string num2 = "";
    char op = 'x';
    rep(i, s.size())
    {
        if (s[i] == '+' || s[i] == '*')
        {
            if (op == 'x')
            {
                op = s[i];
                num1 = num2;
                num2 = "";
            }
            else
            {
                if (op == '*')
                    num1 = to_string(stoi(num1) + stoi(num2));
                else
                    num1 = to_string(stoi(num1) * stoi(num2));
                num2 = "";
                op = s[i];
            }
        }
        else
            num2 += s[i];
    }
    if (op == '*')
        num1 = to_string(stoi(num1) + stoi(num2));
    else
        num1 = to_string(stoi(num1) * stoi(num2));
    cout << num1 << endl;
    return 0;
}