this function should count the "a" in a string and calculate a ratio between the sum of all "a" and the string length. It works fine except when the string is empty and it should output "0" instead of NaN. That'

function ratio(statistic) {
 let charcount = 0 ;
 for ( let i = 0 ; i < statistic.length ; i  ){
   
   if ( statistic[i] == 'a' ){ charcount  = 1 ;}
    
}
return Math.round(charcount/statistic.length * 100) ;
}
console.log(ratio('abababaabaaa'));
console.log(ratio(''));
// 67
// NaN <---- here should be 0

s what I want to fix, thank you.

CodePudding user response：

when you have empty string or null string, the value of statistic.length will be 0. So you are missing of this check in your code that is why you are getting NaN (Not a Number).

function ratio(statistic) {
 let charcount = 0 ;
 for ( let i = 0 ; i < statistic.length ; i  ){
   
   if ( statistic[i] == 'a' ){ charcount  = 1 ;}
    
}
// Corrected code here 
return statistic.length == 0 ? 0 : Math.round(charcount/statistic.length * 100) ;
}
console.log(ratio('abababaabaaa'));
console.log(ratio(''));
// 67
// NaN <---- here should be 0

CodePudding user response：

Try:

function ratio(statistic) {
  let charcount = 0 ;
  for ( let i = 0; i < statistic.length; i   ) {
    if ( statistic[i] == 'a' ) { charcount  = 1; }
  }
  if (charcount === 0) return 0; // check if there were no a's in the string, if so return 0
  return Math.round(charcount/statistic.length * 100) ;
}
console.log(ratio('bbbbbbbaaa'));
console.log(ratio(''));

To prevent from having to divide by 0, we just check if no a's were found and if so return 0 then and there.

CodePudding user response：

You can use a regex to count the amount of matches for the character that you want. (statistic.match(/a/g)||[]).length where you can change 'a' for whatever character (took from here)

The NaN problems is occurring because if the string length is zero, you're dividing 0/0. That's a mathematical indeterminate form. To fix that you should check first if the string is or not empty statistic.length > 0.

let ratio = (statistic) => statistic.length > 0 ? Math.round((statistic.match(/a/g)||[]).length / statistic.length * 100) : 0;

console.log(ratio('abababaabaaa'));
console.log(ratio(''));

CodePudding user response：

If the statistic as a parameter in ratio function is '', statistic.length is 0. And this causes mathematical error because something cannot be divided by 0. If you write some exceptional code like following, it will work well.

function ratio(statistic) {
   let charcount = 0 ;
   for ( let i = 0 ; i < statistic.length ; i  ){
      if ( statistic[i] == 'a' ){ 
         charcount  = 1 ;
      }
   }
   return (statistic == ''? 0 : Math.round(charcount/statistic.length * 100)) ;
}