var sim = [ "mtn", "glo", "airtel"];
var uppercasedCategories = [];

//explicit iteration

for(var i=0; i<sim.length; i=i+1){
  var cash = sim[i];
  if( cash !== undefined) {
      if(cash.indexOf("last") ===0){
        break;
      }
  uppercasedCategories.push(sim[i].toUpperCase());
     
   }
    
}