C Programming: Number sums and their reverses

Last update on August 07 2025 12:49:45 (UTC/GMT +8 hours)

32. Sum with Reverse Expression Variants

Write a C programming to check whether a given integer can be expressed as the sum of any non-negative integer and its reverse. Return true otherwise false.

Example:
Input: = 554
Output: true
Explanation: 371 + 173 = 554
Input: = 51
Output: false
Explanation: It cannot be expressed as per said condition.
Input: = 55
Output: true
Explanation: 41 + 14 = 55
Input: = 181
Output: true
Explanation: 140 + 041 = 181

Test Data:
(554) -> 1
(51) -> 0
(55) -> 1
(181) -> 1

Sample Solution:

C Code:

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

// Function to reverse an integer
int rev(int n){
    int result = 0, t, r;
    for(t = n; n != 0; n = n / 10){
        r = n % 10; // Extracting the rightmost digit of 'n'
        result = result * 10 + r; // Building the reversed number
    }
    return result;
}

// Function to test if a number can be expressed as the sum of any non-negative integer and its reverse
bool test(int n){
    if(n == 0) return true; // If the number is 0, it can be expressed as the sum of itself and its reverse (0)
    for(int i = n / 2; i < n; i++){ // Loop from n/2 to n-1 to find the sum of 'i' and its reverse equal to 'n'
        if(i + rev(i) == n){ // Check if 'i' + its reverse equals 'n'
            return true; // If found, return true
        }
    }
    return false; // If no such 'i' exists, return false
}

// Main function
int main(void) {
    int n = 544;
    printf("n = %d",n);
    printf("\nTest said number can be expressed as the sum of any non-negative integer and its reverse = %d", test(n));
    n = 51;
    printf("\nn = %d",n);
    printf("\nTest said number can be expressed as the sum of any non-negative integer and its reverse = %d", test(n));
    n = 55;
    printf("\nn = %d",n);
    printf("\nTest said number can be expressed as the sum of any non-negative integer and its reverse = %d", test(n));
    n = 181;
    printf("\nn = %d",n);
    printf("\nTest said number can be expressed as the sum of any non-negative integer and its reverse = %d", test(n));
}

Sample Output:

n = 544
Test said number can be expressed as the sum of any non-negative integer and its reverse = 1
n = 51
Test said number can be expressed as the sum of any non-negative integer and its reverse = 0
n = 55
Test said number can be expressed as the sum of any non-negative integer and its reverse = 1
n = 181
Test said number can be expressed as the sum of any non-negative integer and its reverse = 1

Flowchart:

$Flowchart: Number sums and their reverses$

For more Practice: Solve these Related Problems:

Write a C program to check if an integer can be expressed as the sum of a non-negative integer and its reverse.
Write a C program to test numbers for the property of being equal to the sum of a number and its reversed digits.
Write a C program to iterate through potential candidates and verify the sum-with-reverse condition using string reversal.
Write a C program to determine and print all numbers within a range that satisfy the reverse sum property.

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