View Compilation Error

0_0_8850025_18787.c: In function `main':
0_0_8850025_18787.c:1: error: `a' undeclared (first use in this function)
0_0_8850025_18787.c:1: error: (Each undeclared identifier is reported only once
0_0_8850025_18787.c:1: error: for each function it appears in.)