C PROGRAMMING PROGRAM • DECISION MAKING

Check Uppercase or Lowercase Alphabet

Learn how to check uppercase or lowercase alphabet using a clear C program.

Beginnerisupper()islower()Character classification

PROBLEM UNDERSTANDING

Input and expected output

Sample input

Sample output

Lowercase alphabet

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>
#include <ctype.h>

int main(void)
{
    char character;

    printf("Enter an alphabet: ");
    scanf(" %c", &character);
    if (isupper((unsigned char) character))
        printf("Uppercase alphabet\n");
    else if (islower((unsigned char) character))
        printf("Lowercase alphabet\n");
    else
        printf("Not an alphabet\n");
    return 0;
}

CURRENT STEP

Select Start to walk through the important lines.

SELECTED LINE

No line selected

EXPECTED OUTPUT FOR THE SAMPLE

Lowercase alphabet

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Use isupper() and islower() rather than relying on manual ASCII ranges.
Display the computed result.

Use isupper() and islower() rather than relying on manual ASCII ranges.

EFFICIENCY

Time and space complexity

Time complexity

O(1)

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.