C PROGRAMMING PROGRAM • CONTROL FLOW & LOOP FORMS

Validate Positive Input Using goto

Learn how to validate positive input using goto using a clear C program.

IntermediategotoLabelInput validation

PROBLEM UNDERSTANDING

Input and expected output

Sample input

-3
8

Sample output

Invalid input. Try again.
Accepted = 8

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>

int main(void)
{
    int number;
read_again:
    printf("Enter a positive integer: ");
    scanf("%d", &number);
    if (number <= 0) {
        puts("Invalid input. Try again.");
        goto read_again;
    }
    printf("Accepted = %d\n", number);
    return 0;
}

CURRENT STEP

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SELECTED LINE

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EXPECTED OUTPUT FOR THE SAMPLE

Invalid input. Try again.
Accepted = 8

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Jump back to the labelled input statement when validation fails; prefer a loop in normal production code.
Display the computed result.

Jump back to the labelled input statement when validation fails; prefer a loop in normal production code.

EFFICIENCY

Time and space complexity

Time complexity

O(1)

Auxiliary space

O(1)

DEBUGGING CHECKLIST

Common mistakes

Check this

Use the correct format specifier for every variable.

Check this

Initialize variables before using their values.

Check this

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.