View Compilation Error

0_0_36441569_11058.c: In function 'main':
0_0_36441569_11058.c:14:9: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
         for( int i = 0 ; i < len-1 ; i++ )
         ^
0_0_36441569_11058.c:14:9: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code