C Programming: Count common factors of two integers

Last update on August 07 2025 12:49:40 (UTC/GMT +8 hours)

36. Count Common Factors Variants

Write a C program to count common factors of the two given integers.

Factor - A number or algebraic expression that divides another evenly, that is, without leaving a remainder.

Example:
Input: m = 18, b = 6
Factors of 18 are 1, 2, 3, 6, 9, 18
Factors of 18 are 1, 2, 3, 6
Common factors of the said two numbers are - 1,2,3,6
Output: 4

Test Data:
(18, 6) -> 4
(45, 105) -> 4

Sample Solution:

C Code:

#include <stdio.h>
#include <math.h>

// Function to find the number of common factors between two integers x and y
int test(int x, int y) {
  int z, count = 0;

  // Find the smallest number among x and y and assign it to integer z
  if (x > y) {
    z = y;
  } else {
    z = x;
  }

  // Count the common factors of two numbers
  for (int i = 1; i <= z; i++) {
    if (x % i == 0 && y % i == 0) {
      count++; // Increment the count if 'i' is a common factor of both x and y
    }
  }

  return count; // Return the count of common factors
}

// Main function
int main(void) {
  int m = 18;
  int n = 6;
  printf("m = %d, n = %d", m, n);
  printf("\nCommon factors of the said two numbers = %d", test(m, n));

  // Testing with different values
  m = 45;
  n = 105;
  printf("\nm = %d, n = %d", m, n);
  printf("\nCommon factors of the said two numbers = %d", test(m, n));
}

Sample Output:

m = 18, n = 6
Common factors of the said two numbers = 4
m = 45, n = 105
Common factors of the said two numbers = 4

Flowchart:

$Flowchart: Find all prime factors of a given integer$

For more Practice: Solve these Related Problems:

Write a C program to count the common factors of two integers by finding their greatest common divisor first.
Write a C program to list all common factors of two numbers and then count them.
Write a C program to compute common factors efficiently using prime factorization of both numbers.
Write a C program to compare common factor counts for multiple pairs of integers and output a summary.

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