View Compilation Error

0_0_31848504_26975.c: In function 'main':
0_0_31848504_26975.c:5:16: error: 'str' undeclared (first use in this function)
     while(gets(str)){
                ^
0_0_31848504_26975.c:5:16: note: each undeclared identifier is reported only once for each function it appears in