View Compilation Error

0_0_16561801_1320.cpp: In function 'int read()':
0_0_16561801_1320.cpp:6:28: error: 'isdigit' was not declared in this scope
  while(!isdigit(c=getchar()))if(c=='-')t=-1;
                            ^
0_0_16561801_1320.cpp:7:17: error: 'isdigit' was not declared in this scope
  while(isdigit(c))x=x*10+c-'0',c=getchar();
                 ^