C Program To Check Repetition of Digit In A Number using Arrays

Lets write a C program to check if any digit in a user input number appears more than once.

Note: Any positive integer number can be formed using only 0-9 digits. So we take an array with length 10. i.e., 0 to 9

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Source Code: C Program To Check Repetition of Digit In A Number using Arrays

#include<stdio.h>

int main()
{
    int a[10] = {0}, num, rem;

    printf("Enter a positive number\n");
    scanf("%d", &num);

    while(num)
    {
        rem = num % 10;

        if(a[rem] == 1)
            break;
        else
            a[rem] = 1;

        num = num / 10;
    }

    if(num)
        printf("There are repetition of digits in the number\n");
    else
        printf("There are no repetition of digits in the number\n");

    return 0;
}

Output 1:
Enter a positive number
123
There are no repetition of digits in the number

Output 2:
Enter a positive number
156
There are no repetition of digits in the number

Output 3:
Enter a positive number
1232
There are repetition of digits in the number

Logic To Check if any digit in user input number repeats or not

1. Since there are 10 digits i.e., 0 to 9 to form any number, we take array size as 10. We initialize all the elements of array to 0.

Related Read:
Basics of Arrays: C Program

2. We ask the user to input a positive number.

3. We iterate through the while loop until num is zero.

Related Read:
while loop in C programming

4. By modulo dividing user input number by 10, we fetch individual digits of number. We make use of this individual digit as index of the array. We over-write the initial value(which is zero) and assign 1 at that index position.

So presence of value 1 at an index specifies that the digit already exists in the number.

Related Read:
Modulus or Modulo Division In C Programming Language

5. So based on the presence of value 1 or 0 at particular index, our program decides if the digit is present more than once in a number or not.

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