lower case to upper case in c code example

Example 1: C string convert All Uppercse To Lowercase

#include <stdio.h>
#include <string.h>

int main() {
   char s[100];
   int i;

   printf("\nEnter a string : ");
   gets(s);

   for (i = 0; s[i]!='\0'; i++) {
      if(s[i] >= 'A' && s[i] <= 'Z') {
         s[i] = s[i] + 32;
      }
   }

   printf("\nString in Lower Case = %s", s);
   return 0;
}

Example 2: convert string to uppercase in c

For those of you who want to uppercase a string and store it in a variable (that was what I was looking for when I read these answers).

#include <stdio.h>  //<-- You need this to use printf.
#include <string.h>  //<-- You need this to use string and strlen() function.
#include <ctype.h>  //<-- You need this to use toupper() function.

int main(void)
{
    string s = "I want to cast this";  //<-- Or you can ask to the user for a string.

    unsigned long int s_len = strlen(s); //<-- getting the length of 's'.  

    //Defining an array of the same length as 's' to, temporarily, store the case change.
    char s_up[s_len]; 

    // Iterate over the source string (i.e. s) and cast the case changing.
    for (int a = 0; a < s_len; a++)
    {
        // Storing the change: Use the temp array while casting to uppercase.  
        s_up[a] = toupper(s[a]); 
    }

    // Assign the new array to your first variable name if you want to use the same as at the beginning
    s = s_up;

    printf("%s \n", s_up);  //<-- If you want to see the change made.
}
//If you want to lowercase a string instead, change toupper(s[a]) to tolower(s[a]).