View Compilation Error

0_0_27706212_30700.c: In function 'main':
0_0_27706212_30700.c:8:9: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
         for(long long i=0;i<=n;i++)ans+=i;
         ^
0_0_27706212_30700.c:8:9: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code