String Reversal Approaches in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print the reversed string using a loop.

DSA C

char str[] = "hello";
int len = 5;
for (int i = len - 1; i >= [1]; i--) {
    printf("%c", str[i]);
}
printf("\n");

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A0

B1

C-1

Dlen

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 instead of 0 as the loop's stopping condition.

Starting the loop from len instead of len - 1.

The loop should start from the last index (len - 1) and go down to 0 to print all characters in reverse.

2fill in blank

medium

Complete the code to swap characters for in-place string reversal.

DSA C

char str[] = "world";
int len = 5;
for (int i = 0; i < [1]; i++) {
    char temp = str[i];
    str[i] = str[len - i - 1];
    str[len - i - 1] = temp;
}
printf("%s\n", str);

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Alen - 1

Blen

Clen + 1

Dlen / 2

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping characters for the entire length causing double swaps.

Using len instead of len / 2 as the loop limit.

We only need to swap characters up to the middle of the string to reverse it in place.

3fill in blank

hard

Fix the error in the recursive string reversal function call.

DSA C

void reverse(char *str, int start, int end) {
    if (start >= end) return;
    char temp = str[start];
    str[start] = str[end];
    str[end] = temp;
    reverse(str, [1], end - 1);
}

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Aend - 1

Bstart + 1

Cend + 1

Dstart - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Decreasing start instead of increasing it.

Using the same indices causing infinite recursion.

The recursive call should move the start index forward by 1 and the end index backward by 1 to continue swapping.

4fill in blank

hard

Fill both blanks to create a loop that copies characters from the end to the start in a new string.

DSA C

char str[] = "abcde";
char rev[6];
int len = 5;
for (int i = 0; i < [1]; i++) {
    rev[i] = str[[2] - i - 1];
}
rev[len] = '\0';
printf("%s\n", rev);

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Alen

Blen - 1

Clen + 1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using len - 1 as loop limit causing missing last character.

Incorrect index calculation causing wrong characters copied.

The loop runs from 0 to len - 1, and the index for str is len - i - 1 to copy characters in reverse order.

5fill in blank

hard

Fill all three blanks to create a function that returns a new reversed string.

DSA C

char* reverse_string(const char* str) {
    int len = 0;
    while (str[len] != '\0') {
        len++;
    }
    char* rev = malloc(sizeof(char) * (len + 1));
    for (int i = 0; i < [1]; i++) {
        rev[i] = str[[2] - i - 1];
    }
    rev[[3]] = '\0';
    return rev;
}

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Alen

Blen - 1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Not allocating enough memory for the null terminator.

Incorrect loop limits causing incomplete reversal.

The loop runs from 0 to len - 1, copying characters from the end to the start. The null terminator is placed at index len.