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In this example, you will learn to count the number of digits in an integer entered by the user.

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To understand this example, you should have the knowledge of the following C programming topics:

• C Programming Operators
• C while and do…while Loop

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This program takes an integer from the user and calculates the number of digits. For example: If the user enters 2319, the output of the program will be 4.

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Program to Count the Number of Digits

#include 
int main() {
    long long n;
    int count = 0;
    printf("Enter an integer: ");
    scanf("%lld", &n);
 
    // iterate until n becomes 0
    // remove last digit from n in each iteration
    // increase count by 1 in each iteration
    while (n != 0) {
        n /= 10;     // n = n/10
        ++count;
    }

    printf("Number of digits: %d", count);
}

Output

Enter an integer: 3452
Number of digits: 4

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The integer entered by the user is stored in variable n. Then the while loop is iterated until the test expression n! = 0 is evaluated to 0 (false).

• After the first iteration, the value of n will be 345 and the count is incremented to 1.
• After the second iteration, the value of n will be 34 and the count is incremented to 2.
• After the third iteration, the value of n will be 3 and the count is incremented to 3.
• After the fourth iteration, the value of n will be 0 and the count is incremented to 4.
• Then the test expression of the loop is evaluated to false and the loop terminates.