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C Exercises: Check a number is a Happy or not

C Numbers: Exercise-13 with Solution

Write a program in C to check a number is a Happy or not.

Test Data
Input a number: 13

Sample Solution:

C Code:

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


int SumOfSquNum(int givno)
{
    int SumOfSqr = 0;
    while (givno)
    {
        SumOfSqr += (givno % 10) * (givno % 10);
        givno /= 10;
    }
    return SumOfSqr;
}
bool checkHappy(int chkhn)
{
    int slno, fstno;
    slno = fstno = chkhn;
    do
    {
        slno = SumOfSquNum(slno);
        fstno = SumOfSquNum(SumOfSquNum(fstno));
    }
    while (slno != fstno);
    return (slno == 1);
}
int main()
{
int hyno;
	printf("\n\n Check whether a number is Happy number or not: \n");
	printf(" ---------------------------------------------------\n");
	printf(" Input a number: ");
	scanf("%d",&hyno);

    if (checkHappy(hyno))
	printf("%d is a Happy number.\n",hyno);
    else
	printf("%d is not a Happy number.\n",hyno);
}

Sample Output: 

 Input a number: 13                                                                                           
13 is a Happy number.

Pictorial Presentation:

C programming: Check a number is a Happy or not.

Flowchart:

Flowchart: Check a number is a Happy or not

C Programming Code Editor:

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C Programming: Tips of the Day

Why do C and C++ compilers allow array lengths in function signatures when they're never enforced?

It is a quirk of the syntax for passing arrays to functions.

Actually it is not possible to pass an array in C. If you write syntax that looks like it should pass the array, what actually happens is that a pointer to the first element of the array is passed instead.

Since the pointer does not include any length information, the contents of your [] in the function formal parameter list are actually ignored.

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