foo.c: In function 'main':
foo.c:11:16: error: invalid suffix "c" on integer constant
 if ((a[0]+b[0]-2c[n-1])%26==0)
                ^
foo.c:14:21: error: invalid suffix "b" on integer constant
 else if ((a[0]+c[0]-2b[n-1])%26== 0)
                     ^