Format specifiers - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of integer and float formatting

What is the output of this C code snippet?

C

#include <stdio.h>

int main() {
    int a = 42;
    float b = 3.14159;
    printf("%5d %.2f\n", a, b);
    return 0;
}

A 42 3.14

B 42 3.14

C 42 3.1416

D 42 3.14159

💡 Hint

Look at the width and precision in the format specifiers.

The %5d means print the integer right-aligned in a field 5 characters wide, so 42 is padded with 3 spaces. The %.2f means print the float with 2 digits after the decimal point, rounding 3.14159 to 3.14.

❓ Predict Output

intermediate

Output of string and character formatting

What will this C program print?

C

#include <stdio.h>

int main() {
    char c = 'A';
    char *str = "Hi";
    printf("%3c %5s\n", c, str);
    return 0;
}

A A Hi

B A Hi

C A Hi

D iH A

💡 Hint

Check the width specifiers for character and string.

%3c prints the character right-aligned in 3 spaces, so two spaces then 'A'. %5s prints the string right-aligned in 5 spaces, so three spaces then 'Hi'.

❓ Predict Output

advanced

Output with left alignment and zero padding

What is the output of this code?

C

#include <stdio.h>

int main() {
    int x = 7;
    printf("%-5d %05d\n", x, x);
    return 0;
}

A 70000 7

B 7 00007

C 7 7

D 7 00007

💡 Hint

Look at the minus sign and zero in the format specifiers.

%-5d means print integer left-aligned in 5 spaces, so '7' then 4 spaces. %05d means print integer padded with zeros to width 5, so '00007'.

❓ Predict Output

advanced

Output of pointer and hexadecimal formatting

What will this program print?

C

#include <stdio.h>

int main() {
    int num = 255;
    printf("%p %x %X\n", (void*)&num, num, num);
    return 0;
}

A 7ffee3bff6ac ff FF

B 0x7ffee3bff6ac ff FF

C 0x7ffee3bff6ac 0xff 0xFF

D 0x7ffee3bff6ac 255 255

💡 Hint

%p prints pointer with 0x prefix, %x and %X print hex lowercase and uppercase without 0x.

%p prints the pointer address with 0x prefix. %x prints the integer in lowercase hex without 0x. %X prints uppercase hex without 0x. The actual pointer address varies but includes 0x prefix.

❓ Predict Output

expert

Output of mixed format specifiers with precision and width

What is the output of this C program?

C

#include <stdio.h>

int main() {
    double val = 123.456789;
    printf("%10.3f %.5s %04d\n", val, "HelloWorld", 9);
    return 0;
}

A 123.457 Hello 0009

B 123.456789 Hello 0009

C 123.457 HelloWorld 9

D 123.456 Hello 9

💡 Hint

Check width and precision for float, string, and integer.

%10.3f prints float in 10 spaces with 3 decimals, rounding 123.456789 to 123.457. %.5s prints first 5 chars of string "HelloWorld" as "Hello". %04d prints integer padded with zeros to width 4, so 0009.

Practice

1. Which format specifier is used to print an integer value in C using printf?

easy

A. %d

B. %f

C. %c

D. %s

Solution

1. Step 1: Understand integer data type printing

   The %d specifier is used to print integer values in C.

2. Step 2: Identify other specifiers

   %f is for floats, %c for characters, and %s for strings.

3. Final Answer:

   %d -> Option A

4. Quick Check:

   Integer print = %d [OK]

Hint: Use %d for integers in printf [OK]

Common Mistakes:

• Using %f for integers
• Confusing %c with %d
• Using %s for numbers

2. Which of the following is the correct way to print a character variable ch in C?

easy

A. printf("%c", ch);

B. printf("%s", ch);

C. printf("%d", ch);

D. printf("%f", ch);

Solution

1. Step 1: Identify character format specifier

   The correct specifier for a character is %c.

2. Step 2: Check other options

   %s is for strings, %d for integers, and %f for floats, so they are incorrect for a character.

3. Final Answer:

   printf("%c", ch); -> Option A

4. Quick Check:

   Character print = %c [OK]

Hint: Use %c to print single characters [OK]

Common Mistakes:

• Using %s for characters
• Using %d which prints ASCII code
• Using %f for characters

3. What will be the output of the following code?

int x = 10;
float y = 5.5;
printf("%d %f", x, y);

medium

A. 10 5.5

B. 10 5.500000

C. 5.5 10

D. Error

Solution

1. Step 1: Understand format specifiers in printf

   %d prints integer as is, %f prints float with 6 decimal places by default.

2. Step 2: Match variables to specifiers

   x is 10 (int), printed by %d. y is 5.5 (float), printed by %f as 5.500000.

3. Final Answer:

   10 5.500000 -> Option B

4. Quick Check:

   Integer and float print with %d and %f [OK]

Hint: Floats print with 6 decimals by default using %f [OK]

Common Mistakes:

• Expecting %f to print fewer decimals
• Swapping variable order
• Using %d for float causing wrong output

4. Identify the error in the following code snippet:

char name[10];
scanf("%c", name);

medium

A. No error, code is correct

B. Use &name instead of name

C. Use %d instead of %c

D. Use %s instead of %c to read string

Solution

1. Step 1: Understand scanf format specifiers

   %c reads a single character, but name is an array for a string.

2. Step 2: Correct specifier for string input

   To read a string into name, use %s which reads until whitespace.

3. Final Answer:

   Use %s instead of %c to read string -> Option D

4. Quick Check:

   String input needs %s in scanf [OK]

Hint: Use %s to read strings with scanf [OK]

Common Mistakes:

• Using %c to read strings
• Forgetting & with non-array variables
• Using %d for characters

5. You want to print a floating-point number float pi = 3.14159; with only 2 decimal places. Which printf statement is correct?

hard

A. printf("%2f", pi);

B. printf("%f.2", pi);

C. printf("%.2f", pi);

D. printf("%f", pi);

Solution

1. Step 1: Understand precision in format specifiers

   To limit decimal places, use %.2f where 2 is the number of decimals.

2. Step 2: Check other options

   %2f sets minimum width, not decimals; %f.2 is invalid; %f prints 6 decimals by default.

3. Final Answer:

   printf("%.2f", pi); -> Option C

4. Quick Check:

   Use %.2f to print 2 decimals [OK]

Hint: Use %.2f to print float with 2 decimals [OK]

Common Mistakes:

• Using %2f expecting 2 decimals
• Placing .2 after %f incorrectly
• Using %f prints 6 decimals by default