Is String Uppercase Or Lowercase C

Python Programming

Hey there, today we’re going to dive into the world of string manipulation in the C programming language. One common task when working with strings is determining whether a string is in uppercase or lowercase. It’s a fundamental operation that is often required in programming, and C provides several functions to help us with this task.

Checking for Uppercase or Lowercase

One way to check if a string is in uppercase or lowercase in C is to iterate through each character of the string and use the isupper() and islower() functions from the ctype.h header. These functions return non-zero if the character is uppercase or lowercase, respectively.

Here’s a simple example of how to use these functions to check if a string is in uppercase or lowercase:

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

int main() {
char str[] = "Hello";
int isLowerCase = 1;
int isUpperCase = 1;

for(int i=0; str[i]!='\0'; i++) {
if(islower(str[i]) == 0) {
isLowerCase = 0;
if(isupper(str[i]) == 0) {
isUpperCase = 0;

if(isLowerCase == 1) {
printf("The string is in lowercase\n");
} else if(isUpperCase == 1) {
printf("The string is in uppercase\n");
} else {
printf("The string is a mix of uppercase and lowercase\n");

return 0;

Personal Touch

When working on projects, I’ve found that understanding the case of a string is crucial, particularly in scenarios where input validation or formatting is required. Knowing whether a string is in uppercase or lowercase allows for effective error checking and consistent display of data.


Understanding how to determine if a string is in uppercase or lowercase in C is a valuable skill for any programmer. With the help of the isupper() and islower() functions, you can easily perform this check and tailor your code based on the case of the input string. This knowledge has certainly empowered me to write more robust and versatile C programs.