Confusion Converting Hexadecimal to Binary in C++

Question

#include <string>
#include <iostream>

using namespace std;

int main() {
    string input, numBin = ""; 
    cout << "Enter a hexadecimal number: ";
    getline(cin, input);

    for (int i = 0; i < input.length(); i++) {
        switch (input[i]) {
            case 0: numBin.append("0000"); break; 
            case 1: numBin.append("0001"); break;
            case 2: numBin.append("0010"); break;
            case 3: numBin.append("0011"); break;
            case 4: numBin.append("0100"); break;
            case 5: numBin.append("0101"); break;
            case 6: numBin.append("0110"); break;
            case 7: numBin.append("0111"); break; 
            case 8: numBin.append("1000"); break;
            case 9: numBin.append("1001"); break;
            case 'a': numBin.append("1010"); break;
            case 'A': numBin.append("1010"); break;
            case 'b': numBin.append("1011"); break;
            case 'B': numBin.append("1011"); break;
            case 'c': numBin.append("1100"); break;
            case 'C': numBin.append("1100"); break;
            case 'd': numBin.append("1101"); break;
            case 'D': numBin.append("1101"); break;
            case 'e': numBin.append("1110"); break;
            case 'E': numBin.append("1110"); break;
            case 'f': numBin.append("1111"); break;
            case 'F': numBin.append("1111"); break; 
            default: break;
        }
    }
    cout << "Your number in binary is " << numBin << "."; 
}

This program is supposed to change a hexadecimal input ('input') into a binary result ('numBin'). I don't have much experience using switch statements and do not fully understand the "default" case, so any clarification about that or if I am using it incorrectly would be helpful!

The error I'm getting is on the for loop, and it thorws: comparison between signed and unsigned integer expressions [-Wsign-compare]

user2736738 · Answer 1 · 2016-12-31T12:00:40.153

2

case '0':
case '1':
...

Use all characters..not number and characters.

And one ore thing..for(i=0;i<(int) input.length();i++)

edited Dec 31 '16 at 12:00

answered Dec 31 '16 at 11:47

user2736738

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score 2 · Answer 2 · edited May 23 '17 at 11:54

In the line:

for (int i = 0; i < input.length(); i++) ...

input.length() returns a size_t, which is a unsigned type. (see http://www.cplusplus.com/reference/string/string/length/)

Comparing signed and unsigned values is not safe, which is why the compiler warns you, read more about it in this post among many others: A warning - comparison between signed and unsigned integer expressions

To fix it, simply change to

unsigned int i = 0

The default switch case will be executed when none of the other cases match. You should put some code there that handles incorrect input for example.

Confusion Converting Hexadecimal to Binary in C++

2 Answers2