Question

I have recently begun C++ and am trying to understand syntax, but I’m having placement problems. I have to do a credit card validation function that asks for a valid credit card and then I have to print out the type of credit card.

My only issue is with the if-statements for determining the credit card type. I don’t know where exactly to place them and whether or not I’m missing any brackets or such.

The exact chunk that’s problematic for me is:

        if(c.substr(0, 2) == "65" || c.substr(0, 5) == "6011" || c.substr(0, 7) >= "622126" && c.substr(0, 7) <= "622925" || c.substr(0, 4) >= "644" && c.substr(0, 4) <= "649")
            s = "You have a Discover card";
        if(c.substr(0, 2) >= "51" && c.substr(0, 2) <= "55")
            s = "You have a MasterCard card";
        if(c.substr(0, 1) == "4")
            s = "You have a Visa card";
        if(c.substr(0, 2) == "34" || c.substr(0, 2) == "37")
            s = "You have an American Express card"; 

This is my code.

#include <iostream>
#include <string>
using namespace std;

void validateCC();
string checkCC(string, int, bool&);
bool validateCCNum(string);

void main() {
    char again;
    cout << "Validate a credit card number (Y/N)? ";
    cin >> again;
    while (toupper(again) == 'Y') {
        validateCC();
        cout << "Validate a credit card number (Y/N)? ";
        cin >> again;
    }
}

void validateCC() {
    string ccn, msg;
    bool OK;
    int ccLen;
    cout << "Please enter a 15 or 16 digit credit card number."
        << "\n(No spaces or hyphens): ";
    cin >> ccn;
    ccLen = ccn.length();
    msg = checkCC(ccn, ccLen, OK);
    if(!OK)
        cout << msg;
    else
        if(validateCCNum(ccn))
            cout << "Valid credit card number\n";
        else
            cout << "Invalid credit card number\n";
    cout << "\n" << endl;
}

string checkCC(string c, int cLen, bool& ccOK) {
    string s = "";
    ccOK = true;
    for(int i=0;i<cLen && ccOK;++i)
        ccOK = isdigit(c[i]);

        if(c.substr(0, 2) == "65" || c.substr(0, 5) == "6011" || c.substr(0, 7) >= "622126" && c.substr(0, 7) <= "622925" || c.substr(0, 4) >= "644" && c.substr(0, 4) <= "649")
            s = "You have a Discover card";
        if(c.substr(0, 2) >= "51" && c.substr(0, 2) <= "55")
            s = "You have a MasterCard card";
        if(c.substr(0, 1) == "4")
            s = "You have a Visa card";
        if(c.substr(0, 2) == "34" || c.substr(0, 2) == "37")
            s = "You have an American Express card"; 

    if(ccOK == false) {
        s = "Invalid credit card number digits";
    } else if(cLen == 15) {
        if(c.substr(0, 2) != "34" && c.substr(0, 2) != "37") {
            ccOK = false;
            s = "Invalid American Express credit card number";
        }
    } else if(cLen != 16) {
        ccOK = false;
        s = "Invalid credit card number length";
    }
    return s;
}

bool validateCCNum(string cc) {
    bool flip = true;
    int tmp, num = 0;
    int ccLen = cc.length()-1;
    for(int ndx=ccLen;ndx>=0;ndx--) {
            if(flip)
                num += cc[ndx] - '0';
            else {
                tmp = (cc[ndx] - '0') * 2;
                if(tmp <= 9)
                    num += tmp;
                else
                    num += (1 + (tmp - 10)); // max of 18
            }
            flip = !flip;
    }
    return num % 10 == 0;
}

I don’t know whether the problematic chunk belongs where it currently is, or if I place it in the validateCC() section and then add a parameter for it.

Thank you.

Answer 1

Try to change the substrings to int (stringVar >> IntVar;) so you can evaluate the <= >= etc…

    #include <iostream>
#include <string>
using namespace std;

void validateCC();
string checkCC(string, int, bool&);
bool validateCCNum(string);

void main() {
    char again;
    cout << "Validate a credit card number (Y/N)? ";
    cin >> again;
    while (toupper(again) == 'Y') {
        validateCC();
        cout << "Validate a credit card number (Y/N)? ";
        cin >> again;
    }
}
string checkCardType(string c){
if(atoi(c.substr(0, 2).c_str()) == 65 || atoi(c.substr(0, 5).c_str()) == 6011 || atoi(c.substr(0, 7).c_str()) >= 622126 && atoi(c.substr(0, 7).c_str()) <= 622925 || atoi(c.substr(0, 4).c_str()) >= 644 && atoi(c.substr(0, 4).c_str()) <= 649)
            return "You have a Discover card";
        if(atoi(c.substr(0, 2).c_str()) >= 51 && atoi(c.substr(0, 2).c_str()) <= 55)
            return "You have a MasterCard card";
        if(atoi(c.substr(0, 1).c_str()) == 4)
            return "You have a Visa card";
        if(atoi(c.substr(0, 2).c_str()) == 34 || atoi(c.substr(0, 2).c_str()) == 37)
            return "You have an American Express card"; 
        return "Card not recognized";
}
void validateCC() {
    string ccn, msg;
    bool OK;
    int ccLen;
    cout << "Please enter a 15 or 16 digit credit card number."
        << "\n(No spaces or hyphens): ";
    cin >> ccn;
    ccLen = ccn.length();
    msg = checkCC(ccn, ccLen, OK);
    if(!OK)
        cout << msg;
    else
        if(validateCCNum(ccn)){
            cout << "Valid credit card number\n";
            cout << checkCardType(ccn);}
        else
            cout << "Invalid credit card number\n";
    cout << "\n" << endl;
}

string checkCC(string c, int cLen, bool& ccOK) {
    string s = "";
    ccOK = true;
    for(int i=0;i<cLen && ccOK;++i)
        ccOK = isdigit(c[i]);

    if(ccOK == false) {
        s = "Invalid credit card number digits";
    } else if(cLen == 15) {
        if(c.substr(0, 2) != "34" && c.substr(0, 2) != "37") {
            ccOK = false;
            s = "Invalid American Express credit card number";
        }
    } else if(cLen != 16) {
        ccOK = false;
        s = "Invalid credit card number length";
    }
    return s;
}

bool validateCCNum(string cc) {
    bool flip = true;
    int tmp, num = 0;
    int ccLen = cc.length()-1;
    for(int ndx=ccLen;ndx>=0;ndx--) {
            if(flip)
                num += cc[ndx] - '0';
            else {
                tmp = (cc[ndx] - '0') * 2;
                if(tmp <= 9)
                    num += tmp;
                else
                    num += (1 + (tmp - 10)); // max of 18
            }
            flip = !flip;
    }
    return num % 10 == 0;
}