Convert vowels from upper to lower or lower to upper using C program

An array of characters is called a string.

Declaration

Following is the declaration for an array −

char stringname [size];

For example − char a[50]; string of length 50 characters

Initialization

• Using single character constant −

char a[10] = { ‘H’, ‘e’, ‘l’, ‘l’, ‘o’ ,‘\0’}

• Using string constants −

char a[10] = "Hello":;

Accessing

There is a control string "%s" used for accessing the string till it encounters ‘\0’.

The logic used to convert vowels from upper to lower or lower to upper is −

for(i=0;string[i]!='\0';i++){
   if(string[i]=='a'||string[i]=='e'||string[i]=='i'||string[i]=='o'||string[i]=='u'){
      string[i]=toupper(string[i]);
   }
}
printf("The result string with converted vowels is : ");
puts(string);

Program

Following is the C program using conversion functions to convert an Upper case string to Lower case string −

#include<stdio.h>
#include<ctype.h>
void main(){
   //Declaring variable for For loop (to read each position of alphabet) and string//
   int i;
   char string[40];
   //Reading string//
   printf("Enter the string : ");
   gets(string);
   //For loop to read each alphabet//
   for(i=0;string[i]!='\0';i++){
      if(string[i]=='a'||string[i]=='e'||string[i]=='i'||string[i]=='o'||string[i]=='u'){
         string[i]=toupper(string[i]);
      }
   }
   printf("The result string with converted vowels is : ");
   puts(string);
}

Output

When the above program is executed, it produces the following result −

Run 1:
Enter the string : TutoRialsPoint
The result string with converted vowels is : TUtORIAlsPOInt
Run 2:
Enter the string : c programming
The result string with converted vowels is : c programming