View Compilation Error

0_0_18226349_15871.cpp: In function 'int main()':
0_0_18226349_15871.cpp:10:1: error: 'c' was not declared in this scope
 c+=a;
 ^
0_0_18226349_15871.cpp:12:13: error: 'c' was not declared in this scope
 if(2*(i-1)==c)printf("T/n");
             ^