Implicit declaration of functions warning

Question

I'm trying to use the functions isDigit() I have the correct include statement, #include <ctype.h> however, I seem to be getting a warning when I compile,

warning: implicit declaration of function 'isDigit' is invalid in C99 [-Wimplicit-function-declaration]

The line that compiles the warning is if(isDigit(atoi(inputLine)) { can anyone give me feedback as to what I am missing here? Thanks.

Answer 1

The name of the function is isdigit() , not isDigit() . C is case-sensitive.

Answer 2

在你的程序中包含这个头文件： #include<ctype.h>