C Exercises: Find the largest palindrome made from the product of two 3-digit numbers

Last update on May 27 2022 12:16:39 (UTC/GMT +8 hours)

C Programming Practice: Exercise-21 with Solution

2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder.
Write a C programming to find the smallest positive number that is evenly divisible by all of the numbers from 1 to 20?.

C Code:

/* Copyright (c) 2009, eagletmt, Released under the MIT License <https://opensource.org/licenses/mit-license.php> */
#include <stdio.h>
static unsigned long gcd(unsigned long a, unsigned long b);
static __inline unsigned long lcm(unsigned long a, unsigned long b);
int main(void)
{
  unsigned long ans = 1;
  unsigned long i;
  for (i = 1; i <= 20; i++) {
    ans = lcm(ans, i);
  }
  printf("%lu\n", ans);
  return 0;
}
unsigned long gcd(unsigned long a, unsigned long b)
{
  unsigned long r;
  if (a > b) {
    unsigned long t = a;
    a = b;
    b = t;
  }
  while (r = a%b) {
    a = b;
    b = r;
  }
  return b;
}
unsigned long lcm(unsigned long a, unsigned long b)
{
  unsigned long long p = (unsigned long long)a * b;
  return p/gcd(a, b);
}

Sample Output:

232792560

Flowchart:

C Programming Code Editor:

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C Programming: Tips of the Day

Static variable inside of a function in C

The scope of variable is where the variable name can be seen. Here, x is visible only inside function foo().

The lifetime of a variable is the period over which it exists. If x were defined without the keyword static, the lifetime would be from the entry into foo() to the return from foo(); so it would be re-initialized to 5 on every call.

The keyword static acts to extend the lifetime of a variable to the lifetime of the programme; e.g. initialization occurs once and once only and then the variable retains its value - whatever it has come to be - over all future calls to foo().

Ref : https://bit.ly/3fOq7XP