View Compilation Error

0_0_38585035_18104.cpp: In function 'll read()':
0_0_38585035_18104.cpp:12:12: error: 'isdigit' was not declared in this scope
     while(!isdigit(ch)){if(ch=='-')s=-s;ch=getchar();}
            ^~~~~~~
0_0_38585035_18104.cpp:13:11: error: 'isdigit' was not declared in this scope
     while(isdigit(ch)){x=x*10+ch-'0';ch=getchar();}
           ^~~~~~~