C program to convert lowercase vowel to uppercase in string

🧑‍💻 By quescol • 📝 Updated on: 07 May 2025

In this tutorial we will learn writing C program to convert all lowercase vowel to uppercase in given string.

This program is very similar to the program to convert lowercase to uppercase in string using C.

How lowercase vowel to uppercase conversion program works

• Our program will take String as an input.
• Now first using if else we will find the vowel in string. After finding the vowel, If vowel is in lowercase then we will convert it into uppercase.
• And if no vowel then we will not do anything.

C Program to convert lowercase vowel into uppercase of String

#include<stdio.h>
int main()
{
    char str[100];
    int i = 0;
    printf("C Program to Convert lower case vowel to upper case of String  \n");
    printf("Please enter a string: ");
    fgets(str, 100, stdin);
    while( str[i] != '\0' )
    {
        if(str[i]=='a' ||str[i]=='e' ||str[i]=='i' ||str[i]=='o' ||str[i]=='u')
        {
            str[i] = str[i] - 32;
        }
        i++;
    }
    printf("Vowel after converting into upper case = %s ", str);
    return 0;
}

Output

C Program to Convert lower case vowel to upper case of String  
Please enter a string: Quescol Website
Vowel after converting into upper case = QUEscOl WEbsItE

C Program to convert lowercase vowel to Uppercase using  toUpper() function

#include<stdio.h>
#include<ctype.h>
int main()
{
   char str[100];
   printf("C Program to convert lower case vowel to upper case of String \n");
   printf("Please enter a String: ");
   fgets(str, 100, stdin);
   for(int i=0; str[i]!='\0'; i++)
   {
    if(str[i]=='a' ||str[i]=='e' ||str[i]=='i' ||str[i]=='o' ||str[i]=='u'){
        str[i] = toupper(str[i]);
    }
   }
   printf("String after converting into uppercase: %s\n", str);
   return 0;
}

Output

C Program to convert lower case vowel to upper case of String 
Please enter a String: Quescol Website
String after converting into uppercase: QUEscOl WEbsItE