String Traversal and Character Access in DSA C

Mental Model

A string is a sequence of characters stored one after another. Traversing means visiting each character one by one to read or process it.

Analogy: Imagine reading a sentence letter by letter from left to right, like reading a book page from start to end.

S -> t -> r -> i -> n -> g -> \0
↑
(start)

Dry Run Walkthrough

Input: string: "cat"

Goal: Print each character of the string one by one in order

Step 1: Access first character 'c'

c -> a -> t -> \0
↑

Why: Start reading from the first character

Step 2: Access second character 'a'

c -> a -> t -> \0
  ↑

Why: Move to next character to continue reading

Step 3: Access third character 't'

c -> a -> t -> \0
    ↑

Why: Move to next character to continue reading

Step 4: Detect null character '\0' to stop

c -> a -> t -> \0
      ↑

Why: Null character marks end of string, stop traversal

Result:

c\na\nt\n

Annotated Code

DSA C

#include <stdio.h>

void traverseString(const char *str) {
    int i = 0;
    while (str[i] != '\0') { // check for end of string
        printf("%c\n", str[i]); // print current character
        i++; // move to next character
    }
}

int main() {
    const char *myString = "cat";
    traverseString(myString);
    return 0;
}

while (str[i] != '\0') {

check if current character is not end marker to continue traversal

printf("%c\n", str[i]);

print the current character

i++;

advance index to next character

Output

c

a

t

Complexity Analysis

Time: O(n) because we visit each character once until the null terminator

Space: O(1) because we use a fixed number of variables regardless of string size

vs Alternative: Compared to recursive traversal, this iterative approach uses less memory and is simpler

Edge Cases

empty string ""

The loop does not run and nothing is printed

DSA C

while (str[i] != '\0') {

string with one character "a"

Prints the single character then stops

DSA C

while (str[i] != '\0') {

When to Use This Pattern

When you need to process or examine each character in a string one by one, use string traversal with a loop until the null character.

Common Mistakes

Mistake: Forgetting to check for the null character '\0' and causing out-of-bounds access
Fix: Always check str[i] != '\0' before accessing str[i]

Mistake: Using incorrect loop condition like i < length without knowing string length
Fix: Use null character check to safely traverse strings of unknown length

Summary

It visits each character in a string one by one until the end.

Use it when you want to read or process every character in a string.

The null character '\0' marks the end and stops traversal.