Pointers & Strings

How Pointers Work With Strings

A string can be represented in two ways:

• Using a character array
• Using a pointer to char

char s1[] = "Hello";    // Stored in array
char *s2 = "Hello";     // Pointer to constant string literal

Pointer Traversal in Strings

You can move a pointer through a string using increments.

char name[] = "Sourav";
char *p = name;

while(*p != '\0'){
    printf("%c ", *p);
    p++;
}

Pointer Arithmetic With Strings

• p + 1 → moves to next character
• p + n → jumps n characters
• *p → gives current character

Common Pointer–String Operations

• Traverse string
• Count characters
• Compare two strings
• Copy one string to another
• Modify string characters

Example: String Length Using Pointer

#include <stdio.h>

int main(){
    char s[] = "WebTech";
    char *p = s;
    int count = 0;

    while(*p){
        count++;
        p++;
    }

    printf("Length = %d", count);
    return 0;
}

Example: Modify Characters Using Pointer

#include <stdio.h>

int main(){
    char s[] = "Sahu";
    char *p = s;

    p[0] = 'R';   // change first letter

    printf("%s", s);
    return 0;
}

Pointer vs Array Indexing

• s[i] is same as *(s + i)
• Pointers give faster string access
• Used in most library functions internally

Pointers & Strings – 10 Examples

1. Print String Using Pointer

#include <stdio.h>

int main() {
    char *p = "Hello World";
    printf("%s", p);
    return 0;
}

2. Access Characters Using Pointer

#include <stdio.h>

int main() {
    char name[] = "Sourav";
    char *p = name;

    printf("%c %c %c", *p, *(p+1), *(p+2));
    return 0;
}

3. Modify String Using Pointer

#include <stdio.h>

int main() {
    char word[] = "Cat";
    char *p = word;

    p[0] = 'B';

    printf("%s", word);  // Bat
    return 0;
}

4. Count Length Using Pointer

#include <stdio.h>

int main() {
    char s[] = "Pointers";
    char *p = s;
    int len = 0;

    while(*p != '\0') {
        len++;
        p++;
    }

    printf("Length: %d", len);
    return 0;
}

5. Count Vowels Using Pointer

#include <stdio.h>

int main() {
    char s[] = "Education";
    char *p = s;
    int count = 0;

    while(*p) {
        char ch = *p;
        if(ch=='a'||ch=='e'||ch=='i'||ch=='o'||ch=='u'||
           ch=='A'||ch=='E'||ch=='I'||ch=='O'||ch=='U')
            count++;
        p++;
    }

    printf("Vowels: %d", count);
    return 0;
}

6. Compare Two Strings Using Pointer

#include <stdio.h>

int strcompare(char *a, char *b) {
    while(*a && *b) {
        if(*a != *b) return 0;
        a++; b++;
    }
    return (*a == '\0' && *b == '\0');
}

int main() {
    printf("%d", strcompare("abc", "abc"));
    return 0;
}

7. Reverse String Using Pointer

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

int main() {
    char s[] = "Sourav";
    int i = 0, j = strlen(s) - 1;
    char t;

    while(i < j) {
        t = s[i];
        s[i] = s[j];
        s[j] = t;
        i++; j--;
    }

    printf("%s", s);
    return 0;
}

8. Convert to Uppercase Using Pointer

#include <stdio.h>

int main() {
    char s[] = "hello";
    char *p = s;

    while(*p) {
        if(*p >= 'a' && *p <= 'z') {
            *p = *p - 32;
        }
        p++;
    }

    printf("%s", s);
    return 0;
}

9. Copy String Using Pointer

#include <stdio.h>

void copy(char *d, char *s) {
    while(*s) {
        *d = *s;
        d++; s++;
    }
    *d = '\0';
}

int main() {
    char src[] = "India";
    char dest[20];

    copy(dest, src);
    printf("%s", dest);

    return 0;
}

10. Find Frequency of Character

#include <stdio.h>

int main() {
    char s[] = "programming";
    char *p = s;
    char ch = 'm';
    int count = 0;

    while(*p) {
        if(*p == ch)
            count++;
        p++;
    }

    printf("Frequency: %d", count);
    return 0;
}

Where Pointer-String Handling Is Used?

• Text editors
• Input validation
• Token parsing
• Command-line arguments
• File names and paths

Practice Questions

1. Explain relation between pointers and strings.
2. Why can't we modify string literals?
3. How can you traverse a string using a pointer?
4. Difference between char s[] and char *s?
5. Write pointer-based string length logic.

Practice Task