Question

Following is a simple program which implements a DFA(deterministic finite automata). However, my problem does not involve DFA.

#include<iostream>
using namespace std;

int main()
{
    char c;
    int state=1;
    while((c=cin.get())!='4')
    {
        switch(state)
        {
            case 1:
            if(c=='0')
            state=2;
            if(c=='1')
            state=1;
            if(c=='2')
            state=2;

            break;

            case 2:
            if(c=='0')
            state=5;
            if(c=='1')
            state=1;
            if(c=='2')
            state=3;

            break;

            case 3:
            if(c=='0')
            state=1;
            if(c=='1')
            state=5;
            if(c=='2')
            state=4;

            break;

            case 4:
            if(c=='0')
            state=3;
            if(c=='1')
            state=4;
            if(c=='2')
            state=5;

            break;

            case 5:
            if(c=='0')
            state=5;
            if(c=='1')
            state=4;
            if(c=='2')
            state=1;

            break;

            default:
            cout<<"Input will not be accepted"<<endl;

        } //switch
        cout<<"Current state is "<<state<<endl; 
    } //while


    return 0;
}

When I ran the code, I found that every line was being output twice. For, example when I entered 0 1 0 0 4, the DFA goes from state 1->2->1->2->5 and thus output should be:

Current state is 2
Current state is 1
Current state is 2
Current state is 5

But the output is:

Current state is 2
Current state is 2
Current state is 1
Current state is 1
Current state is 2
Current state is 2
Current state is 5
Current state is 5

Can anyone point out the cause?

Answer 1

cin.get() reads one character, so you are also reading spaces. Then after each space your program just outputs previous state because space doesn’t match anything. You want to use cin >> c instead.