View Compilation Error

0_0_37317416_31665.c: In function 'main':
0_0_37317416_31665.c:7:3: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
   for(int i = 1; i <= x; i++) sum+=i;
   ^
0_0_37317416_31665.c:7:3: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code