foo.cpp: In function 'int main()':
foo.cpp:18:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 for (k = 0; k <a.size(); k++) { if ((a[k] >= '0') && (a[k] <= '9'))
                       ^
foo.cpp:21:13: error: expected ';' before numeric constant
 p[t] = p[t] 10 + (int)(a[k] - '0');
             ^
foo.cpp:38:14: error: expected ';' before 'x'
 x = y + p[k] x;
              ^
foo.cpp:59:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 for (k = 0; k < a.size(); k++)
                        ^