tolower() Function not Working in C99

c cs50 tolower
ChapmIndustries picture ChapmIndustries · Sep 27, 2012 · Viewed 11.2k times · Source

I am using the CS50 appliance from Harvard and trying to make a character lowercase. I am trying to use the tolower() function but when I try to use it I get the message implicit declaration of function 'tolower' is invalid in C99. Anyone care to elaborate on why I would be getting this message. I have included stdio.h as well as string.h.

Answer

Gabe picture Gabe · Sep 27, 2012

To use tolower in C99, use #include <ctype.h>

It is not an I/O function and it doesn't operate on strings (it operates on characters), so it's not in stdio or string.

Related questions

What do .c and .h file extensions mean to C?

It's all in the title; super-simple I reckon, but it's so hard to search for syntactical things anywhere. These are two library files that I'm copying from CS50.net, and I'm wondering why they have two different extensions.

Read More
C - Undefined symbols for architecture x86_64 when compiling on Mac OSX Lion

I'm getting some problems on compiling a very very simple name.c file on Mac OSX Lion. Now, I started following Harvard CS50 course on cs50.net. I'm not totally new to programming but I was curious on how this …

Read More
*Beginner* C: incompatible integer to pointer conversion passing 'char' to parameter of type 'const char *'

I'm trying to convert each letter in a string to it's ASCII number. Using int letter = (atoi(ptext[i])); gives me this error: error: incompatible integer to pointer conversion passing 'char' to parameter of type 'const char *'; take the …

Read More