The value of the term - the solution

#include <iostream>
#include<string>
using namespacestd;

int main()
{
string iz,s1,s2;
    getline( cin, iz );

    int poz[4];
//Returns the position of the computational operation or -1 if it is not found
    poz[0]=iz.find("+");
    poz[1]=iz.find("-");
    poz[2]=iz.find("*");
    poz[3]=iz.find("/");
int i=0, p, q;
while(poz[ i ]==-1){
        i++;
    }
    q=i;

    p=poz[i];
//numbers in the form of a string
    s1=iz.substr(0,p);
    s2=iz.substr(p+1);

//Convert numbers to int data
int a=0, b=0;
for(int i=0;i<s1.length();i++){
char ch= s1.at(i);                          //character from the string at the i-th position, eg. ch = 3
int c=ch-'0';                                     // c= '3' - '0', the difference of the codes of these digits is 3
        a=10*a+c;

    }

for(int i=0;i<s2.length();i++){
char ch= s2.at(i);
int c=ch-'0';
        b=10*b+c;
    }

switch(q){     //selection of the switch based on the value of the integer variable q, which represents
        case 0: cout<<a+b<<endl; break;            //calculation operation​
        case 1: cout<<a-b<<endl; break;
        case 2: cout<<a*b<<endl; break;
        case 3: cout<<a/b<<endl;
    }

return 0;
}