Why does this for-loop only run once?

Question

The goal of my code: To be able to write a program where I can enter in any number int as a command-line argument and displays how many digits in the integer number are 7s.

My problem is that I don't understand why my code only runs through the for-loop once. I inserted the system.out.println(sevens); to see how many times this loop works when I compile with a random number like 456789.

I could only think of a for-loop to use for this one and fixed some simple mistakes in the beginning. I also checked my brackets

public class TestingSevens {
    public static void main(String[] args) {
        int sevens = Integer.parseInt(args[0]);

        int count = 0;

        for (int i = 0; i < args.length; i++) {
            if (sevens%10 == 7) {
                count += 1;
            }
            sevens = sevens/10;
            System.out.println(sevens);
        }
        System.out.println(count);
    }
}

The result of inputting a number like 456789 is "45678" for the first print and the second print is "0." I know the number for some reason only runs through the loop once since it cuts off the last number before jumping out of the loop to print the count...any advice?

Answer 1

I presume you want to iterate over each digit of sevens . Since sevens initialized from args[0] , the loop limit should match and look at args[0].length() rather than args.length .

for (int i = 0; i < args[0].length(); i++)

An alternate way to write the loop is to iterate until sevens reaches 0. That lines up better with the loop body; both use the same variable.

while (sevens > 0) {
    if (sevens%10 == 7) {
        count += 1;
    }
    sevens /= 10;
    System.out.println(sevens);
}

Answer 2

Your code has logic errors, so to check if the iterated number is number 7 you need to turn the number into a string and check if the character is the desired character using: numberString.charAt(index)

Below is the corrected code:

public static void main(String[] args) {

    int sevens = Integer.parseInt(args[0]);
    String numberString = String.valueOf(sevens);
    int count = 0;

    for (int i = 0; i < numberString.length(); i++) {
        char c = numberString.charAt(i);        

        if (c == '7') {
            count += 1;
        }

        System.out.println("Input number: " + sevens);
    }
    System.out.println("Count of 7 numbers: " + count);
}