How to Write a C Program to Find the Integer with the Largest Sum of Digits Until -1 is Entered

In this article, we will guide you through writing a C program that prompts the user to enter integers one by one until they input -1. The program will then identify and print the number that has the largest sum of its digits. We will walk through the steps, provide a complete C program, and explain how to compile and run it.

Steps to Create the Program

Initialize Variables: Create variables to store the current number, the maximum sum of digits, and the corresponding number with the largest sum of digits. Input Loop: Continuously read integers from the user until they enter -1. Sum of Digits Calculation: Implement a function to calculate the sum of the digits of a given integer. Track the Largest Sum: Update the variables that track the largest sum and the corresponding number as you read each new integer. Output: Print the number with the largest sum of digits after the user enters -1.

Complete C Program

Function: sum_of_digits(int num)

This function calculates the sum of the digits of a given integer.

#include stdio.h
int sum_of_digits(int num) {
    int sum  0;
    num  num  0 ? -num : num; // Convert negative numbers to positive
    while (num  0) {
        sum   num % 10; // Add the last digit to the sum
        num / 10;       // Remove the last digit
    }
    return sum;
}

Main Function: int main(void)

int main(void) {
    int number;
    int max_sum  -1; // To store the maximum sum of digits
    int number_with_max_sum  0; // To store the corresponding number
    printf(Enter integers (enter -1 to stop):);
    while (1) {
        scanf(%d, number);
        if (number  -1) {
            break; // Exit the loop if -1 is entered
        }
        int current_sum  sum_of_digits(number);
        if (current_sum  max_sum) {
            max_sum  current_sum;
            number_with_max_sum  number; // Update the number with the largest sum of digits
        }
    }
    if (max_sum ! -1) { // Check if at least one valid number was entered
        printf(The number with the largest sum of digits is %d (%d)
, number_with_max_sum, max_sum);
    } else {
        printf(No valid numbers were entered.
);
    }
    return 0;
}

Explanation of the Code

Function sum_of_digits: Converts negative numbers to positive, then iteratively extracts and sums the digits of the number. Main Function: Initializes variables, prompts the user for input, and processes each number in the loop. If the sum of the digits of the current number is greater than the previous maximum, it updates the maximum and the corresponding number. Output: After the loop, the program prints the number with the largest sum of digits if any valid numbers were entered; otherwise, it prints a message indicating no numbers were entered.

Compiling and Running the Program

To compile and run the program, you can use a C compiler like gcc. Here are the commands you would use in a terminal:

gcc -o sum_of_digits_program sum_of_digits_program.c ./sum_of_digits_program

Replace sum_of_digits_program.c with the actual name of your C file.

Conclusion

This C program provides a straightforward solution to identifying the number containing the largest sum of digits from a series of user inputs until the user enters -1. Understanding and implementing this program can help you gain experience with C programming, input/output handling, and basic algorithmic reasoning.