Help with Limiting Input

I need help with Limiting the user input to only 4 digits and each digit can only be 0-7. It's an encryption program that takes replaces each digit with (sum of the digit + 3)modulus 8. Then swaps the first digit with the second and the third with the fourth. I have a problem with my program allowing numbers with less and more than 4 digits. I can't properly create an if statement.
This is my code.

#include <cstdlib>
#include <iostream>

void encryptSwap(int,int,int,int);

using namespace std;

int main(){
    
    int num;
    //Prompt user to input 4 digit number
    cout<<"Enter 4 digit number to be Encrypted"<<endl;
    cin>>num;

    //Variables for each digit
    int d1,d2,d3,d4;

    //Grab each individual digit
    d1=num%10000;
    d1=d1/1000;
    d2=num%1000;
    d2=d2/100;
    d3=num%100;
    d3=d3/10;
    d4=num%10;

    //Check value
    if((d1>=0&&d1<=7)&&(d2>=0&&d2<=7)&&(d3>=0&&d3<=7)&&(d4>=0&&d4<=7)){
      encryptSwap(d1,d2,d3,d4);
    }else{
       cout<<"Value is Invalid!"<<endl;
    }
return 0;
}
void encryptSwap(int digit1,int digit2,int digit3,int digit4){
    //Replace value
    digit1=(digit1+3)%8;
    digit2=(digit2+3)%8;
    digit3=(digit3+3)%8;
    digit4=(digit4+3)%8;

    //Swap Values
    //Value place holder variables
    int x, y;
    x=digit2;
    y=digit4;
    digit2=digit1;
    digit1=x;
    digit4=digit3;
    digit3=y;
    //Display encrypted number
    cout<<"Encrypted number:"<<endl;
    cout<<digit1<<digit2<<digit3<<digit4<<endl;
}

I can't figure out how to keep it only 4 digits with each digit only being 0-7.

jlb (4973)

Have you considered getting the input as a char? Then as part of the input validation convert these characters to your int?

Last edited on

ForRealzZzZ (22)

Your problem is std::cin grabs all 4 digits then you try to grab the numbers individually that cin has placed in num

d1=num%10000;
    d1=d1/1000;
    d2=num%1000;
    d2=d2/100;
    d3=num%100;
    d3=d3/10;
    d4=num%10;

What you are actually doing is this:

    d1=num%10000;//d1 still equals num
    d1=d1/1000;
    d2=num%1000;//d2 equals num as well
    d2=d2/100;
    d3=num%100;//d3 is num
    d3=d3/10;
    d4=num%10;//surprise its num D:

To fix this you could split them up into four separate variables

cin>>d1;
cin>>d2'
cin>>d3;
cin>>d4;

Unless you overload another operator and make your own cin type function or use bitshift algorithms this function wont work.

Last edited on

Kurisutofaa (23)

So something like this.

    char num[4];
    int d1,d2,d3,d4;
    cout<<"Enter 4 digit number"<<endl;
    cin>>num
    
    d1=(int)num[0]-48;
    d2=(int)num[1]-48;
    d3=(int)num[2]-48;
    d4=(int)num[3]-48;

I can still accept 5 digits with this though.

fg109 (709)

ForRealzZzZ wrote:

What you are actually doing is this:

    d1=num%10000;//d1 still equals num
    d1=d1/1000;
    d2=num%1000;//d2 equals num as well
    d2=d2/100;
    d3=num%100;//d3 is num
    d3=d3/10;
    d4=num%10;//surprise its num D:

I think he had it working the way it was...

    //let's say num = 9876
    d1=num%10000; //d1 = 9876
    d1=d1/1000; //d1 = 9
    d2=num%1000; //d2 = 876
    d2=d2/100; //d2 = 8
    d3=num%100; //d3 = 76
    d3=d3/10; //d3 = 7
    d4=num%10; //d4 = 6

@Kurisutofaa

Try using cin.getline(num, 4);.
http://cplusplus.com/reference/istream/istream/getline/

GaGoKoYa (50)

char num[3]; ---> 0 1 2 3
if (d1 > 7 || ...) ---> get another input

Last edited on

Kurisutofaa (23)

Thanks for the help guys. I got it working properly.

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