C Program to convert uppercase string to lowercase string

In the following C program, user would be asked to enter a String (it can be in complete uppercase or partial uppercase) and then the program would convert it into a complete(all characters in lower case) lower case string. The logic we have used in the following program is: All the upper case characters (A-Z) have ASCII value ranging from 65 to 90 and their corresponding lower case characters (a-z) have ASCII value 32 greater than them. For example ‘A‘ has a ASCII value 65 and ‘a‘ has a ASCII value 97 (65+32). Same applies for other characters.

 
/* C program to convert uppercase string to
 * lower case
 * written by: Chaitanya
 */
#include<stdio.h>
#include<string.h>
int main(){
   /* This array can hold a string of upto 25
    * chars, if you are going to enter larger string
    * then increase the array size accordingly
    */
   char str[25];
   int i;
   printf("Enter the string: ");
   scanf("%s",str);
 
   for(i=0;i<=strlen(str);i++){
      if(str[i]>=65&&str[i]<=90)
         str[i]=str[i]+32;
   }
   printf("\nLower Case String is: %s",str);
   return 0;
}

Output:

As you can see in the output that we have entered a partial (only few chars were in upper case) upper case string and the program output was a complete lower case string.