c++ - Curly brackets after for statement -

i'm newbie. wrote code print sum of number 1 10. here's happened;

for(a = 1; a<=10; a++) sum += a; cout<<sum; 

executing gave me correct answer i.e 55

when execute following:

for(a = 1; a<=10; a++) { sum += a; cout<<sum; } 

it gives me complete different , wrong answer i.e 13610152128364555

why happen? goes wrong when put curly brackets after statement?

i hope not silly question.

if break apart big number:

1 3 6 10 15 21 28 36 45 55 

you can see what's happening - it's outputting accumulated sum after every addition, because cout within loop. it's hard see because have no separator between numbers.

you'll see difference if format code properly:

for(a = 1; a<=10; a++)     sum += a;             // done each loop iteration cout<<sum;                // done once @ end.  for(a = 1; a<=10; a++) {     sum += a;             // done each loop iteration     cout<<sum;            // done each loop iteration }