C Programming: Convert a string to uppercase

Last update on August 06 2025 13:02:32 (UTC/GMT +8 hours)

21. Convert String to Uppercase

Write a program in C to convert a string to uppercase.

Sample Solution:

C Code:

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

int main() {
    int ctr=0; // Variable to keep track of position in the string
    char str_char; // Variable to store each character of the string
    char str[100]; // Array to store the input string

    printf("\n Convert a string to uppercase. :\n");
    printf("-----------------------------------");
    printf("\n Input a string in lowercase : ");
    fgets(str, sizeof str, stdin); // Read a string including spaces from the user

    printf(" Here is the above string in UPPERCASE :\n ");

    while (str[ctr]) { // Loop through each character of the string until the null character is encountered
        str_char = str[ctr]; // Retrieve each character from the string
        putchar(toupper(str_char)); // Convert the character to uppercase using toupper() function and print it
        ctr++; // Move to the next character in the string
    }

    printf("\n\n");
    return 0; // Return 0 to indicate successful execution of the program
}

Output:

 Convert a string to uppercase. :
-----------------------------------
 Input a string in lowercase : the quick brown fox jumps over the lazy dog.
 Here is the above string in UPPERCASE :
 THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG.

Flowchart:

Flowchart: Convert a string to uppercase

For more Practice: Solve these Related Problems:

Write a C program to convert a given string to uppercase without using the toupper() function.
Write a C program to traverse a string and convert each lowercase letter to uppercase using ASCII arithmetic.
Write a C program to convert only the alphabetic characters of a string to uppercase while leaving digits unchanged.
Write a C program to transform a sentence to uppercase and then count the total number of uppercase letters.

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C Programming Code Editor:

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