String helpers

Add and test string processing functions.

String helpers

The second lesson defines str_len and str_is_empty. str_len returns the byte count of a string; str_is_empty tells whether the string is empty.

For str_len you walk to the end of the string and count characters. str_is_empty calls str_len and compares the result to zero. This avoids code duplication: a single length function serves both length and emptiness checks. The main from the previous lesson is included in the starting code; you add the new functions.

str_len implementation

str_len walks to the end of the string and counts. The most natural form is a while (*s) loop; at the string end *s becomes zero and the loop exits.

Example: int str_len(const char *s) { int n = 0; while (*s) { n++; s++; } return n; }. Each step increments n and advances s. The loop stops at '\0'. This pattern is common in C; the standard strlen works similarly.

Exercise Add str_len and str_is_empty

Below the existing declarations, write int str_len(const char *s); count the string length with a while (*s) loop and return it. Write int str_is_empty(const char *s) that returns str_len(s) == 0. In main add printf("%d\n", str_len("Merhaba")); and printf("%d\n", str_is_empty(""));.

Show example solution

#include <stdio.h>

int str_len(const char *s);
int str_is_empty(const char *s);
int num_abs(int n);
int num_sign(int n);
int arr_max(int *a, int n);
int arr_sum(int *a, int n);

int str_len(const char *s) {
    int n = 0;
    while (*s) { n++; s++; }
    return n;
}

int str_is_empty(const char *s) {
    return str_len(s) == 0;
}

int main(void) {
    printf("Modül hazır\n");
    printf("%d\n", str_len("Merhaba"));
    printf("%d\n", str_is_empty(""));
    return 0;
}

Test yourself

Match the string helpers

str_len("Merhaba")

7 (string length)
str_len("")

0 (empty string)
str_is_empty("")

1 (empty)
str_is_empty("x")

0 (non-empty)
Which loop is most natural for str_len?
- while (*s)
- do...while
- for (int i=0; i<n; i++)
- switch
Show answer

while (*s) — while (*s) walks to the string end; it's the natural choice.

Complete the str_len loop

int str_len(const char *s) {
    int n = 0;
    while (____) { n++; s++; }
    return n;
}

Show answer

int str_len(const char *s) {
    int n = 0;
    while (*s) { n++; s++; }
    return n;
}

Next lesson: Number helpers

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