Main.cc: In function ‘int main()’: Main.cc:11:5: error: expected ‘,’ or ‘;’ before ‘while’ while(a[i]=='A'||a[i]=='T'||a[i]=='G'||a[i]=='C'){ ^~~~~ Main.cc:10:9: warning: unused variable ‘i’ [-Wunused-variable] int i=0 ^