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    #include <stdio.h>

    void functionupper(char []);

    int main()
    {
       char string[100];

       printf("Enter a string to convert it into upper case\n");
       gets(string);

       functionupper(string); // calling functionupper

       printf("Entered string in upper case is \"%s\"\n", string);

       return 0;
    }

    void functionupper(char s[]) {
       int c = 0;

       while (s[c] != '\0') {
          if (s[c] >= 'a' && s[c] <= 'z') {
             s[c] = s[c] - 32;
          }
          c++;
       }
    }