Wstep

int isNumber(string thing){
    for(int i=0; i<thing.length(); i++){
        if( thing[i]!=45 &&  (thing[i]<48 || thing[i]>57))
            return 0;
    }
    return 1;
}

int checkFile(){
    string nr;
    if(!file.good()){
        cout<<"Brak pliku data.txt"<<endl;
        return 0;
    }

    for(int i=0; true; i++){
        file >> nr;
        //fscanf(file, "%s\n", &nr);
        //printf("%d %s ", i+1, nr);

        //cout<<nr<<" : "<<isNumber(nr)<<endl;
        if(file.eof()){
            //cout<<"h"<<endl;
            return i;
        }

        if(!isNumber(nr)){
            //cout<<nr<<endl;
            return 0;
        }
    }
}

void loadFile(int tab[]){
    int fileSize=checkFile();
    //cout<<fileSize<<endl;
    if(fileSize){
        //fclose(file);
        fstream f;
        f.open("data.txt");
        for(int i=0; i<arraySize; i++){
            f >> tab[i];
            //fscanf(f, "%d\n", &numbers[i]);
        }
        //fclose(f);
    }else{
        error++;
        cout<<"dane nieprawidlowe"<<endl;
    }
}

void keyboard(int tab[]){
    for (int i = 0; i < arraySize; i++) {
        string z;
        cin>>z;
        if (isNumber(z)==1){
            stringstream geek(z);
            int x ;
            geek >> x;
            tab[i]=x;
        }else{
            error++;
            printf("Niepoprawna wartosc wprowadzona");
            break;
        }
    }
}