String handling using library functions - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of string concatenation with strcat

What is the output of this C program?

C

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

int main() {
    char str1[20] = "Hello";
    char str2[] = " World";
    strcat(str1, str2);
    printf("%s", str1);
    return 0;
}

A Compilation error

B Hello

C Hello World

D WorldHello

💡 Hint

Remember that strcat appends the second string to the first one.

The function strcat appends str2 to the end of str1. Since str1 has enough space, the result is "Hello World".

❓ Predict Output

intermediate

Result of strlen on a string

What is the output of this C program?

C

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

int main() {
    char str[] = "C programming";
    printf("%zu", strlen(str));
    return 0;
}

A 12

B 14

C Compilation error

D 13

💡 Hint

strlen counts characters before the null terminator.

The string "C programming" has 13 characters including the space. strlen returns 13.

❓ Predict Output

advanced

Output of strcmp comparing two strings

What is the output of this C program?

C

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

int main() {
    char s1[] = "apple";
    char s2[] = "apples";
    int result = strcmp(s1, s2);
    printf("%d", result);
    return 0;
}

A 0

B A negative number

C A positive number

D Compilation error

💡 Hint

strcmp returns negative if first string is less than second.

Since "apple" is shorter and lexicographically less than "apples", strcmp returns a negative value.

❓ Predict Output

advanced

Behavior of strcpy with overlapping strings

What is the output of this C program?

C

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

int main() {
    char str[] = "overlap";
    strcpy(str + 2, str);
    printf("%s", str);
    return 0;
}

A Undefined behavior (may crash or print garbage)

B ovoverlap

C laplap

D overlap

💡 Hint

strcpy does not support overlapping source and destination.

Using strcpy with overlapping source and destination causes undefined behavior. The output may vary or crash.

🧠 Conceptual

expert

Which function safely copies strings with buffer size limit?

Which of the following C functions is designed to copy strings safely by limiting the number of characters copied to avoid buffer overflow?

A strncpy

B strcpy

C strcat

D strcmp

💡 Hint

One function lets you specify the maximum number of characters to copy.

strncpy copies up to a specified number of characters, helping prevent buffer overflow. strcpy does not limit copying.