C PROGRAMMING PROGRAM • CONTROL FLOW & LOOP FORMS

Create a Countdown Using a while Loop

Learn how to create a countdown using a while loop using a clear C program.

Beginnerwhile loopDecrementCondition

PROBLEM UNDERSTANDING

Input and expected output

Sample input

Sample output

5 4 3 2 1 Go!

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>

int main(void)
{
    int number;
    printf("Enter starting number: ");
    scanf("%d", &number);
    while (number >= 1) {
        printf("%d ", number);
        number--;
    }
    puts("Go!");
    return 0;
}

CURRENT STEP

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SELECTED LINE

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EXPECTED OUTPUT FOR THE SAMPLE

5 4 3 2 1 Go!

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Test the condition before each iteration and reduce the counter until it reaches zero.
Display the computed result.

Test the condition before each iteration and reduce the counter until it reaches zero.

EFFICIENCY

Time and space complexity

Time complexity

O(n)

Auxiliary space

O(1)

DEBUGGING CHECKLIST

Common mistakes

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Use the correct format specifier for every variable.

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Initialize variables before using their values.

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Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.