C code doesn't work, but no errors shown

Question

I am preparing for my Computer Science practical examination, when I hit this roadblock. The following C code is to capitalize all the words in a string taken from the user.

#include<stdio.h>
#include<string.h>
#include<ctype.h>

int main()
{
    char a[20];
    int i;
    printf("Enter a string: ");
    scanf("%[^\n]s",a);

    if(islower(a[0])!=0)
    {
        a[0]=toupper(a[0]);
    }

    for(i=0;i<strlen(a);i++)
        if(a[i]==' ' && isalpha(a[i+1]!=0))
            a[i+1]=toupper(a[i+1]);

    printf("%s\n",a);
    return 0;
}

But the above code doesn't perform the task. It takes the input, but gives the same output(the entered string, as is). Also, there are no errors or warnings shown. I am coding in Ubuntu 14.04 using gcc. I don't seem to understand as to why the code doesn't work.

Answer 1

Your error is with isalpha(a[i+1]!=0), as you should simply check isalpha(a[i+1]). The return-value of the expression a[i+1]!=0 is 1 for all the characters in the input string, except for the last one. The return-value of isalpha(1) is 0, and so the statement under the if condition will execute only for the last character, and only if that character is preceded by a space character.

Having said that, here is a better way for you to implement the whole thing:

for (i=1; a[i]!=0; i++)
    if (a[i-1]==' ' && isalpha(a[i]))
        a[i] = toupper(a[i]);

Answer 2

Should your block :

if(islower(a[0])==0)
{
   a[0]=toupper(a[0]);
}

be checking that it is not equal to zero rather than it is?

Answer 3

check the first ) in isalpha(a[i+1]!=0)),its misplaced.

for(i=0;i<strlen(a);i++)
    if(a[i]==' ' && isalpha(a[i+1])!=0)
        a[i+1]=toupper(a[i+1]);

also the first if should be

if(islower(a[0]){}