title: toupper tolower
body: <p>How to use topper and tolower in the C language?
  I've tried to run the program that I've made, it runs properly
  the problem is since I should submit it to a website to check it whether it's right or wrong, every time I submit it, it says compile error.</p>
  
  <p>I made the code on macbook, using Xcode and it says on my toupper and tolower code -- implicit declaration of function 'toupper' is invalid in C99</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include &lt;string.h&gt;
  int main()
  {
      int input;
      scanf("%d",&amp;input);
      int jumlahkata;
  
      char kalimat[100];
  
      for(int i=0;i&lt;input;i++)
      {
          scanf("%s",kalimat);
          jumlahkata=strlen(kalimat);
          for(int j=0;j&lt;jumlahkata;j++)
          {
              if(j%2==0 || j==0)
              {
                  kalimat[j]=toupper(kalimat[j]);
              }
              else
              {
                  kalimat[j]=tolower(kalimat[j]);
              }
          }
          printf("%s\n",kalimat);
      }
  
      return 0;
  }
  </code></pre>