Common string operations - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of string length calculation

What is the output of this C code snippet?

C

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

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

A 8

B 11

C 10

D 9

💡 Hint

Remember that strlen counts characters before the null terminator.

The string "Hello, C!" has 9 characters including the comma and space but excluding the null terminator.

❓ Predict Output

intermediate

Result of string concatenation with strcat

What will be printed by this C program?

C

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

int main() {
    char s1[20] = "Code";
    char s2[] = "Master";
    strcat(s1, s2);
    printf("%s", s1);
    return 0;
}

A Code Master

B MasterCode

C Code

D CodeMaster

💡 Hint

strcat appends the second string to the first one.

strcat adds the contents of s2 to the end of s1, resulting in "CodeMaster".

❓ Predict Output

advanced

Output of string comparison

What is the output of this C code?

C

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

int main() {
    char a[] = "apple";
    char b[] = "apricot";
    int result = strcmp(a, b);
    if (result < 0) {
        printf("A");
    } else if (result > 0) {
        printf("B");
    } else {
        printf("C");
    }
    return 0;
}

A A

B B

C Compilation error

D C

💡 Hint

strcmp returns a negative value if the first string is lexicographically less.

"apple" is lexicographically less than "apricot", so strcmp returns a negative number and prints "A".

❓ Predict Output

advanced

Behavior of strcpy with overlapping strings

What happens when this C code runs?

C

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

int main() {
    char str[] = "OverlapTest";
    strcpy(str + 3, str);
    printf("%s", str);
    return 0;
}

A OverlapTestOverlapTest

B Undefined behavior (may print corrupted string)

C OverTest

D Compilation error

💡 Hint

strcpy does not support overlapping source and destination.

Using strcpy with overlapping memory causes undefined behavior, so output may be corrupted or unpredictable.

🧠 Conceptual

expert

Correct use of snprintf to avoid buffer overflow

Which option correctly uses snprintf to safely copy a string into a fixed-size buffer without overflow?

A snprintf(buffer, sizeof(buffer), "%s", source);

B snprintf(buffer, strlen(source), "%s", source);

C snprintf(buffer, sizeof(source), "%s", source);

D snprintf(buffer, sizeof(buffer) - 1, "%s", source);

💡 Hint

Use the buffer size, not the source length, to limit snprintf.

Option A uses the buffer size to limit snprintf, preventing overflow and ensuring null termination.