Tokenizing a string - c

Question

I am in the process of writing a C program that parses a string and tokenizing it by breaking the string characters into words that are seperated by white space. My question is when i run my current program:
#include <stdio.h>
#include <stdlib.h>
int main()
{
char input[20];
printf("Please enter your word:\n");
scanf("%c", &input);
printf("%c", input[1]);
return 0;
}
If i was to enter the word "This", i would expect to get back "h" when i run the program but instead i get a downwards pointing arrow. However, when the input is set to print out input[0] i get back a "T".
Edit: I have modified my code so that it prints out the whole string now which i will show below
int main()
{
char input[20];
printf("Please enter your words:\n");
scanf("%s", input);
printf("%s", input);
return 0;
}
My goal is to be able to break that string into chars that i can search through to find whitespace and thus being able to isolate those words for example, if my input was "This is bad" i'd like the code to print out
This
is
bad
Edit:
I have modified my code to fit one of these answers but the problem i run into now is that it won't compile
int main()
{
char input[20];
printf("Please enter your words:\n");
size_t offset = 0;
do
{
scanf("%c", input + offset);
offset++;
}
while(offset < sizeof(input) && input[offset - 1] != '\n');
}
printf("%c", input[]);
return 0;

Answer 1

Problems:
1) scanf("%c", input); only set the first element of the array input.
2) printf("%c", input[1]); prints the second element of the array input, which has uninitialized data in it.
Solution:
Small state machine. No limit on string size like 20.
#include <ctype.h>
#include <stdio.h>
int main() {
int ch = fgetc(stdin);
while (ch != EOF) {
while (isspace(ch)) {
// If only 1 line of input allowed, then add
if (ch == '\n') return 0;;
ch = fgetc(stdin);
}
if (ch != EOF) {
do {
fputc(ch, stdout);
ch = fgetc(stdin);
} while (ch != EOF && !isspace(ch));
fputc('\n', stdout);
}
}
return 0;
}

Answer 2

scanf("%c", &input); does not do what you think it does.
First of all, %c scans only a single character: http://www.cplusplus.com/reference/cstdio/scanf/
Second, array's name is already a pointer to it's first element, so stating &input you make a pointer to a pointer, so instead of storing your character in array's first element you store it in pointer to the array which is a very bad thing.
If you really want to use scanf, I recommend a loop:
size_t offset = 0;
do
{
scanf("%c", input + offset);
offset++;
}
while(offset < sizeof(input) && input[offset - 1] != '\n');
Using scanf("%s", input") leaves you vulnerable to buffer overflow attacks if the word is longer than 20 characters http://en.wikipedia.org/wiki/Buffer_overflow
In my example I assumed, that you want to finish your word with a newline character.
EDIT: In scanf documentation is also a good example:
scanf("%19s", input);
It scans no more than 19 characters, which also prevent buffer overflow. But if you want to change input size, you have to change it two places.

Answer 3

You can use
char * strtok ( char * str, const char * delimiters );
to tokenize your string. If you have your input in input[] array and want to tokenize the string accoring to whitespace character, you can do the following :
char *ptr;
ptr = strtok(input, " ");
while(ptr != NULL) {
printf("%s\n", ptr);
ptr = strtok(NULL, " ");
}
Only the first call to strtok() requires the character array as input. Specifying NULL in the next calls means that it will operate on the same character array.

Answer 4

Your scanf only picks up the first character, input[1] contains random garbage. Use scanf("%19s", input) instead.