View Compilation Error

0_0_33340339_31966.c: In function 'main':
0_0_33340339_31966.c:8:1: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
 for(int i=0; i<2*n; ++i) 
 ^
0_0_33340339_31966.c:8:1: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code
0_0_33340339_31966.c:15:1: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
 for(int i=0; i<2*n; ++i)
 ^
0_0_33340339_31966.c:20:9: error: redefinition of 'i'
 for(int i=0; i<2*n; ++i)
         ^
0_0_33340339_31966.c:15:9: note: previous definition of 'i' was here
 for(int i=0; i<2*n; ++i)
         ^
0_0_33340339_31966.c:20:1: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
 for(int i=0; i<2*n; ++i)
 ^