Adding a number into a string in C

Question

I have the following code snippets:

student_t students[10];
char *name = "Student";

and this one

for (int i = 0; i < STUDENT_COUNT; i++) {
    students[i].id = i;
    students[i].note = 1.0 + (i%4);
    strcpy(students[i].name, name);
    students[i].name[7] = (char) i + '0';  
    students[i].name[8] = '\0';           
}

I dont understand this part:

    students[i].name[7] = (char) i + '0';  
    students[i].name[8] = '\0';

What is happening here?

(char) i + '0' That converts an int single digit to an ascii character. 0 becomes '0', 1 becomes '1', etc. — kaylum
– kaylum, Commented Nov 10, 2020 at 20:28
It's writing the character which represents the single digit value i (with '0' + i) and then terminating the string (with '\0'). — Weather Vane
– Weather Vane, Commented Nov 10, 2020 at 20:28
If i is a number from 0 to 9, then it can be represented by ASCII characters from '0' to '9'. And in order it to do so, it needs to get offset by the ascii value of '0'. — Eugene Sh.
– Eugene Sh., Commented Nov 10, 2020 at 20:29
Can you please show the definition of STUDENT_COUNT? If it is greater than 9 then that code won't work. — kaylum
– kaylum, Commented Nov 10, 2020 at 20:30
Presumably that is the hard-coded 10 in student_t students[10];. Please do fully use your macros – there should be a single definition of sizes, limits etc where possible. — Weather Vane
– Weather Vane, Commented Nov 10, 2020 at 20:31

ikegami · Accepted Answer · 2020-11-10 20:41:01Z

students[i].name[7] = (char) i + '0';

i + '0' converts the numbers 0 to 9 into the ASCII encoding of those numbers.^[1]

0 ⇒ '0'
1 ⇒ '1'
...
9 ⇒ '9'

students[i].name[8] = '\0';

C strings must be terminated by a NUL character ('\0' aka just 0).

The buffer to which name points:

+-----+-----+-----+-----+-----+-----+-----+-----+
| 'S' | 't' | 'u' | 'd' | 'e' | 'n' | 't' |  0  |
+-----+-----+-----+-----+-----+-----+-----+-----+

students[i].name:

Initial:

+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+- ... -+-----+
| ??? | ??? | ??? | ??? | ??? | ??? | ??? | ??? | ??? | ??? |       | ??? |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+- ... -+-----+

After strcpy(students[i].name, name);:

+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+- ... -+-----+
| 'S' | 't' | 'u' | 'd' | 'e' | 'n' | 't' |  0  | ??? | ??? |       | ??? |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+- ... -+-----+

After students[i].name[7] = (char) i + '0'; (when i==4):

+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+- ... -+-----+
| 'S' | 't' | 'u' | 'd' | 'e' | 'n' | 't' | '4' | ??? | ??? |       | ??? |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+- ... -+-----+

After students[i].name[8] = '\0';:

+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+- ... -+-----+
| 'S' | 't' | 'u' | 'd' | 'e' | 'n' | 't' | '4' |  0  | ??? |       | ??? |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+- ... -+-----+

On an EBCDIC machine, it will produce the EBCDIC encoding of the number.

Collectives™ on Stack Overflow

Adding a number into a string in C

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related