Learning Flutter - flutter

Question

I am Ali from Senegal. I am 60 years old(maybe this is my real problem - smiley!!!).
I am learning Flutter and Dart. Today I wanted to use a list of given data model (it's name is Mortalite, please see in the code below).
I try to use dartpad. I am very sad because I do not understand why the following snipet does not run:
//https://www.dartpad.dev/
void main(){
print('Beginning');
List<Mortalite>pertes;
var causes = ['Bla0', 'Bla1', 'Bla2', 'Bla3'];
var lstDate = ['21/09/2020', '22/09/2020', '23/09/2020', '24/09/2020'];
var perteInst = [2, 4, 3, 1];
var total=0;
for (int i = 0; i < 4; i++) {
total += perteInst[i];
print(i); // prints only '0'
pertes[i] = new Mortalite(
causesPerte: causes[i],
datePerte: lstDate[i],
perteInstant:perteInst[i],
totalPertes: total);
};
print(pertes.length); // nothing printed
print('Why?'); // nothing printed
}
class Mortalite {
String datePerte;
String causesPerte;
int perteInstant; // pertes du jour
int totalPertes; // Total des pertes.
Mortalite(
{this.datePerte,
this.causesPerte,
this.perteInstant,
this.totalPertes}
);
}
Thank you well for help.
A.KOTE

Answer 1

The reason above code doesn't work is because you have List pertes initialized and you are passing to the elements of pertes. When you try to pass to 0 index of pertes, it cannot find it and it throws range error because pertes doesn't have an index 0 yet. Please take a look at fix below and let me know if you need help with anything.
void main(){
print('Beginning');
List<Mortalite>pertes=[];
var causes = ['Bla0', 'Bla1', 'Bla2', 'Bla3'];
var lstDate = ['21/09/2020', '22/09/2020', '23/09/2020', '24/09/2020'];
var perteInst = [2, 4, 3, 1];
var total=0;
for (int i = 0; i < causes.length; i++) {
total += perteInst[i]; // prints only '0'
pertes.add (new Mortalite(
causesPerte: causes[i],
datePerte: lstDate[i],
perteInstant:perteInst[i],
totalPertes: total));
};
print(pertes.length); // nothing printed // nothing printed
}
class Mortalite {
String datePerte;
String causesPerte;
int perteInstant; // pertes du jour
int totalPertes; // Total des pertes.
Mortalite(
{this.datePerte,
this.causesPerte,
this.perteInstant,
this.totalPertes}
);
}