View Compilation Error

0_0_6003822_32498.c: In function `main':
0_0_6003822_32498.c:19: error: `a' undeclared (first use in this function)
0_0_6003822_32498.c:19: error: (Each undeclared identifier is reported only once
0_0_6003822_32498.c:19: error: for each function it appears in.)
0_0_6003822_32498.c:25: error: syntax error before '!' token