Some task

#include<iostream>
#define maxSize 10
using namespace std;

struct NUM {
    int sign = 1;
    int data [maxSize] = {0};
};
NUM diff(NUM a, NUM b);
NUM sum(NUM a, NUM b);

void printNum(NUM number) {
    if(number.sign == -1) {
        cout<<"-";
    }
    bool flag = false;
    for(int i = 0; i < maxSize; i++) {
        if(number.data[i]!=0) {
            flag = true;
        }
        if(flag == true) {
            cout<<number.data[i];
        }
    }
    if(flag == false) {
        cout<<"0";
    }
}
NUM convertToNum(string s) {
    NUM number;
    int i = 0;
    if(s[0]=='-') {
        number.sign = -1;
        i = 1;
    } else {
        number.sign = 1;
    }
    for(i; i < s.size(); i++) {
        number.data[maxSize - s.size() + i] = s[i] - '0';
    }
    return number;
}

NUM sum(NUM a, NUM b) {
    NUM c;
    if(a.sign==b.sign) {
        for(int i = maxSize - 1; i >= 0; i--) {
            c.data[i] = c.data[i]+a.data[i]+b.data[i];
            if(c.data[i]>9) {
                c.data[i]-=10;
                c.data[i-1] = 1;
            }
        }
        c.sign = a.sign;
    }
    if(a.sign!=b.sign) {
        a.sign*= -1;
        c = diff(a, b);
        c.sign*= -1;
    }

    return c;
}

int compareNum(NUM a, NUM b) {
    if(a.sign == 1 && b.sign ==-1) {
        return 1;
    }
    if(a.sign == -1 && b.sign == 1) {
        return -1;
    }
    for(int i = 0; i < maxSize; i++) {
        if(a.sign == 1 && b.sign == 1 && a.data[i] > b.data[i] || a.sign == -1 && b.sign == -1 && a.data[i] < b.data[i]) {
            return 1;
        } else if(a.sign == 1 && b.sign ==1&& a.data[i] < b.data [i]||a.sign == -1 && b.sign== -1 && a.data[i] > b.data[i] ) {
            return -1;
        }
    }
    return 0;
}
void swap (NUM a, NUM b) {
    NUM c = b;
    b = a;
    a = c;
}
NUM difHelp(NUM a, NUM b) {
    NUM c;
    c.sign = 1;
    for(int i = maxSize -1 ; i >= 0; i--) {
        c.data[i] = c.data[i]+ a.data[i] - b.data[i];
        if(c.data[i] < 0) {
            c.data[i] += 10;
            c.data[i-1] = -1;
        }
    }
    return c;
}
NUM diff( NUM a, NUM b) {
    NUM c ;
    if(a.sign == 1 && b.sign == 1 && compareNum(a,b) == -1 || a.sign == -1 && b.sign == -1 && compareNum(a,b) == 1 ) {
        c = difHelp(a,b);
        c.sign = -1;
    }
    if(a.sign == -1 && b.sign == 1 && compareNum(a,b) == 1 || a.sign == -1 && b.sign == 1 && compareNum (a, b) == -1) {
        c = sum(a,b);
        c.sign = -1;
    }
    if(a.sign == 1 && b.sign == -1 && compareNum(a,b) == 1 || a.sign == 1 && b.sign == -1 && compareNum (a, b) == -1) {
        c = sum(a, b);
        c.sign = 1;
    }
    if(a.sign == 1 && b.sign == 1 && compareNum(a,b) == 1 ) {
        c = difHelp(a,b);
        c.sign = 1;
    }
    if(a.sign == -1 && b.sign == -1 && compareNum(a,b) == -1 ) {
        c = difHelp(b, a);
        c.sign = 1;
    }

    return c;
}
NUM mult10(NUM a) {
    for(int i = 0; i <= maxSize-2; i++) {
        a.data[i] = a.data[i+1];
    }
    a.data[maxSize-1] = 0;
    return a;
}
NUM multShort(NUM a, int p) {
    NUM c;
    for(int i = maxSize - 1; i >= 1; i--) {
        c.data[i] = c.data[i] + a.data[i]*p;
        if(c.data[i] > 9) {
            c.data[i-1] = c.data[i]/10;
            c.data[i] = c.data[i]%10;
        }
    }
    return c;
}
NUM mult(NUM a, NUM b) {
    NUM ans, t;

    int digits = 0;
    while(b.data[digits] == 0) digits++;
    for(int i = maxSize - 1; i >= maxSize - digits; i-- ) {
        t = multShort(a, b.data[i]);
        ans = sum(ans, t);
        a = mult10(a);
    }
    if(a.sign == b.sign) {
        ans.sign = 1;
    } else {
        ans.sign = -1;
    }
    return ans;
}

NUM zero() {
    NUM a;
    for (int i = 0; i < maxSize; i++)
        a.data[i] = 0;
    return a;
}

NUM one() {
    NUM a = zero();
    a.data[maxSize - 1] = 1;
    return a;
}

bool isZero(NUM a) {
    for (int i = 0; i < maxSize; i++) {
        if (a.data[i] != 0) return false;
    }
    return true;
}

bool isOne(NUM a) {
    for (int i = 0; i < maxSize - 1; i++) {
        if (a.data[i] != 0) return false;
    }
    return (a.data[maxSize - 1] == 1);
}

NUM divByTwo(NUM a) {
    for (int i = 0; i < maxSize; i++) {
        if (i + 1 < maxSize)
            a.data[i + 1] += 10 * (a.data[i] % 2);
        a.data[i] /= 2;
    }
    return a;
}

NUM div(NUM a, NUM b) {
    NUM c;
    int cmp = compareNum(a,b);
    if(isZero(a)) {
        return zero();
    }
    if(cmp == 0) {
        return one();
    }
    if(isOne(b)) {
        return a;
    }

    NUM rB = a, lB = one(), mid, prevC = zero();
    do {
        prevC = mid;
        mid = divByTwo(sum(rB, lB));
        NUM res = mult(b, mid);
        printNum(res);
        cout << endl;
        cmp = compareNum (a,res);
        if(cmp == 1) {
            lB = mid;
        } else {
            rB = mid;
        }
    } while(cmp && compareNum(mid, prevC));
    if(a.sign == b.sign) {
        mid.sign = 1;
    } else {
        mid.sign = -1;
    }
    return mid;
}
int main() {
    NUM a = convertToNum("1902");
    NUM b = convertToNum("112");
    NUM c = diff(a, b);
    NUM d = sum(a, b);
    NUM f = mult(a, b);
    NUM e = div(a, b);
    printNum(a);
    cout << " - ";
    printNum(b);
    cout << " = ";
    printNum(c);
    cout<<endl;
    cout<<"----------------------"<<endl;
    printNum(a);
    cout << " + ";
    printNum(b);
    cout << " = ";
    printNum(d);
    cout<<endl;
    cout<<"----------------------"<<endl;
    printNum(a);
    cout<<" * ";
    printNum(b);
    cout<<" = ";
    printNum(f);
    cout<<endl;
    cout<<"----------------------"<<endl;
    printNum(a);
    cout<<" / ";
    printNum(b);
    cout<<" = ";
    printNum(e);
    return 0;
}