C PROGRAMMING PROGRAM • LOOPS & NUMBER PROBLEMS

Reverse an Integer Using a Loop

Learn how to reverse an integer using a loop using a clear C program.

Beginnerwhile loopDigit extractionReverse

PROBLEM UNDERSTANDING

Input and expected output

Sample input

-12045

Sample output

Reversed = -54021

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>

int main(void)
{
    long long number, value, reversed = 0;

    printf("Enter an integer: ");
    scanf("%lld", &number);
    value = number < 0 ? -number : number;
    while (value > 0) {
        reversed = reversed * 10 + value % 10;
        value /= 10;
    }
    if (number < 0) reversed = -reversed;
    printf("Reversed = %lld\n", reversed);
    return 0;
}

CURRENT STEP

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SELECTED LINE

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EXPECTED OUTPUT FOR THE SAMPLE

Reversed = -54021

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Shift the reversed value left by one decimal place and append each extracted digit.
Display the computed result.

Shift the reversed value left by one decimal place and append each extracted digit.

EFFICIENCY

Time and space complexity

Time complexity

O(d)

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.