Checking if string is only letters and spaces - arrays

Question

I wrote this simple code to check if a string is letters and spaces only
#include<stdio.h>
#include<conio.h>
#include<math.h>
#include<stdlib.h>
#include<string.h>
#define N 100
int checkString(char str1[]);
void main()
{
char str1[N];
scanf("%s", str1);
printf("%d",checkString(str1));
getch();
}
int checkString(char str1[])
{
int i, x=0, p;
p=strlen(str1);
for (i = 0; i < p ; i++)
{
if ((str1[i] >= 'a' && str1[i] <= 'z') || (str1[i] >= 'A' && str1[i] <= 'Z') || (str1[i] == ' '))
{
continue;
}
else{ return 0; }
}
return 1;
}
This works fine when I type something like :
hello asds //returns 1
hello1010 sasd // return 0
but if I type anything after space it returns 1, like this :
hello 1220 //returns 1
blabla 11sdws // returns 1
Can someone please tell me why?

Answer 1

The function can be written more simpler and correctly if to use standard C functions isalpha and isblank declared in header <ctype.h> For example
#include <ctype.h>
//...
int checkString( const char s[] )
{
unsigned char c;
while ( ( c = *s ) && ( isalpha( c ) || isblank( c ) ) ) ++s;
return *s == '\0';
}
If you want to check whether a string contains white spaces then instead of function isblank you should use function isspace.
Take into account that it is not a good idea to use statement continue in such simple loops. It is better to rewrite the loop without the continue statement.
And instead of function scanf it is better to use function fgets if you want to enter a sentence The function allows to enter several words as one string until the Enter will be pressed.
For example
fgets( str1, sizeof( str1 ), stdin );
Take into account that the function includes the new line character. So after entering a string you should remove this character. For example
size_t n = strlen( str1 );
if ( n != 0 && str1[n-1] == '\n' ) str1[n-1] = '\0';

Answer 2

You forgot about the numbers
int checkString(char str1[]) {
int i, x=0, p;
p=strlen(str1);
for (i = 0; i < p ; i++)
if ((str1[i] >= 'a' && str1[i] <= 'z') || (str1[i] >= 'A' && str1[i] <= 'Z') || (str1[i] == ' ') || (str1[i] >= '0' && str1[i] <= '9')) {
continue;
} else return 0;
return 1;
}
Or better
#include <ctype.h>
...
int checkString(char str1[]) {
int i, x=0, p;
p=strlen(str1);
for (i = 0; i < p ; i++)
if (isalnum(str1[i]) || (str1[i] == ' '))
continue;
else return 0;
return 1;
}

Answer 3

This is happening because you are taking input with scanf(%s,&str). In this way of input only characters before space \n or other whitespace characters are stored. So your when you enter space the input is stored only upto space.
eg, you input helloo 1234
Your str stores only helloo and 1234 remains in buffer. Try using getchar().
#include<stdio.h>
#include<conio.h>
#include<math.h>
#include<stdlib.h>
#include<string.h>
#define N 100
int checkString(char str1[]);
void main()
{
char str1[N];
int i=0;
while(1)
{
str1[i++]=getchar();
if(str1[i-1]=='\n') break;
}
printf("%d",checkString(str1));
getch();
}
int checkString(char str1[])
{
int i, x=0, p;
p=strlen(str1);
for (i = 0; i < p ; i++)
{
if ((str1[i] >= 'a' && str1[i] <= 'z') || (str1[i] >= 'A' && str1[i] <= 'Z') || (str1[i] == ' '))
{
continue;
}
else{ return 0; }
}
return 1;
}

Answer 4

When you use scanf("%s",str1);,you input hello 112,what str1 gets is hello.So you can use fgets(str1,N,stdin); to get the string.I think it will work.

Answer 5

There is a problem with your input String
scanf() which will take your input up to space only as it is whitespace
So when you input as hello 1234 actual input it is checking is hello . Check this by printing what you are taking input (that is print str1). Then you will come to know mistake in this code.
You can use gets or fgets to solve the problem.

Answer 6

if you print back the string you just scanf()ed you will notice that it only gets the first portion of all inputs. i.e. anything after the white space including the white space is ignored.
you could use getch() (windows) or getchar() (linux) to get every char input and terminate when you have a "\n" (newline)
source: http://www.cplusplus.com/reference/cstdio/scanf/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#define N 100
int checkString(char str1[]);
void main()
{
int i = 0;
int c;
char str1[N];
memset(str1, 0, sizeof(str1));
do {
c = getchar();
str1[i++] = c;
} while ((c != '\n') && (i < (N - 1))); // (i < N - 1) reserves one place for null char
// last char is '\n' - remove it.
str1[i-1] = 0;
printf("Result: %s\n", checkString(str1) ? "letters and/or spaces only" : "other characters other than spaces and/or letters present");
}
// expects a null terminated string
int checkString(char str1[])
{
char* p = str1;
while (*p) {
if (!isalpha(*p) && !isspace(*p)) {
return 0;
}
p++;
}
return 1;
}