i wrote this prog but it giving me different result,where am i wrong at?

Question

int a[4]={1,2,34,56};
for (int b=0 ; b<4 ; b++){
a[b]=100;
cout<<b << ":" <<a[b] <<endl;
}
result;
1:100
2:100
and instead of 34=100 its giving me 3=100

Answer 1

It's totally normal: an array is indexed by successively interger numbers starting from 0...
First element is always 0, then 1, 2, 3... and so on...
So your result, in reality, is:
0:100
1:100
2:100
3:100
If you want arbitrary indexes, you'll need to use a map like ( array of associative (key, value) pair ) instead of a basic array ;)

Answer 2

That's because you assign a new value before you printed it. Try this:
int a[4]={1,2,34,56};
for (int b=0 ; b<4 ; b++){
cout<<a[b] << ":";
a[b]=100;
cout<<a[b]<<endl;
}