In the below code what does the statements str1[i] && str2[i]; and count1[str1[i]]++; do exactly ?
char str1[4]="rate";
char str2[4]="tear";
int count1[256] ;
int count2[256] ;
int i=0;
for (i = 0; str1[i] && str2[i]; i++)
{
count1[str1[i]]++;//count1['g']++what does that mean ?
count2[str2[i]]++;
}
for (i = 0; str1[i] && str2[i]; i++)
is the same as
for (i = 0; (str1[i] != 0) && (str2[i] != 0); i++)
which is the same as
for (i = 0; (str1[i] != '\0') && (str2[i] != '\0'; i++)
Basically if any expression is used in a conditional statement, then the value is checked for boolean - true or false. If it's not a boolean - say it's an integral type, then 0 is false anything else is true.
Here str[i] is a char - which is an integral type. So if str[i] is 0, then it evaluates to false, else it evaluates to true.
For eg.
char c = 'A';
if(c)
is the same as
if (c != 0)
which is the same as
if (c != '\0')
c is 'A' (which in ascii is 65). 65 != 0, hence it evaluates to true & the if will be entered.
if instead, you have
char c = 0;
or
char c = '\0';
then c evaluates to 0. Hence if(c) evaluates to false & the if is not entered.
You can extend the same logic to str[i] which is an char.
If you have str1[]="rate", it's the same as
str1[0] = 'r', str1[1] = 'a', str1[2] = 't', str1[3] = 'e', str1[4] = 0.
About the count1[str1[i]]++;
It's a count of how many times each character occurs - for eg. if the char set is ascii, then at the end of string traversal, count['A'] (which is the same as count[65]) will contain the number of times 'A' occurred in the string.
It will work only if each member of the count arrays are initialized to 0 somewhere (or they are global).
consider
str1[] = "ABAB";
count[str1[0]] is same as count['A'] which is same as count[65] (if char set is ascii).
The ++ will cause count['A'] to become 1
When i becomes 1, count[str1[1]]++ causes count['B'] to become 1.
i = 2, then count['A'] becomes 2.
i = 3, then count['B'] becomes 2.