Member Avatar for DelilahDemented

I'm working on a problem where I am trying to validate the user input to verify only digits have been used. I'm trying to use the ASCII code to do so, but I'm stuck. I would greatly appreciate any help that can be provided. Thank you in advance!!!

*Delilah*

#include <iostream> 
using namespace std; 
int main() 
{ 
    char number[11]; 
    int x = 0; 
    cout << "Please enter the phone number: "; 
    cin >> number; 
    while (number[x] != '\0')
    { 
        if ((int(number[x]) > 46 || int(number[x]) < 58)
        cout << int(number[x]); 
        x++; 
    } 
 else
    {
        cout << "Invalid characters";
    }//end if
 
    system("pause");
    return 0; 
}
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  • Latest Post Latest Post by Taywin

Dani AI

Generated

Nice start, . As hinted, the logic needs an AND and matching braces, and is right about the digit range. But you do not need raw ASCII at all. Prefer the standard character checks: use std::isdigit (cast to unsigned char before calling to avoid UB) and drive the validation with std::all_of. It is clearer, safer, and stops early on the first bad character. (en.cppreference.com)

#include <iostream>
#include <string>
#include <algorithm>
#include <cctype>

bool all_digits(const std::string& s) {
    return !s.empty() &&
           std::all_of(s.begin(), s.end(),
                       [](unsigned char ch){ return std::isdigit(ch); });
}

int main() {
    std::string number;
    std::cout << "Please enter the phone number: ";
    std::getline(std::cin, number);

    if (all_digits(number) && number.size() == 10)
        std::cout << "Valid\n";
    else
        std::cout << "Invalid characters\n";
}

If you later want to allow formatting like dashes or spaces, first normalize: build a new string containing only the digits, then verify it has exactly 10. Keep using std::isdigit with an unsigned char argument to avoid undefined behavior with negative char values on some platforms. (en.cppreference.com)

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Member Avatar for jonsca

There are a few options and probably some others that I have forgotten about.

The easiest is to keep the program like you have it (although you have a mismatch in the if/else pair which needs to be fixed) and after you've stepped through the char array with the while loop, compare x to 10, if the 2 are equal it's a valid number. Check the condition of your if statement because it's incorrect, you want numbers that sit in between 46 and 58 rather than anything >46 OR <58.

Another option is to change number to an integer and use the fail bit of the input stream (see second code sample on this site http://www.cs.utk.edu/cs102/lectures/cinLecture.html). If any alpha characters are put in the stream will fail and you can check for that and loop back for more input.

There's also strtol (include <cstdlib>) which can be used on your char array input and the function will return a value if there's a successful conversion. See

Member Avatar for Taywin

I think '0' is 48 (x30) in ASCII code? so the condition should be >47 && <58 instead?

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