Multiple input and output in C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read two integers from the user.

C

#include <stdio.h>

int main() {
    int a, b;
    printf("Enter two numbers: ");
    scanf([1], &a, &b);
    printf("You entered %d and %d\n", a, b);
    return 0;
}

Drag options to blanks, or click blank then click option'

A"%d %d"

B"%s %s"

C"%c %c"

D"%f %f"

Attempts:

3 left

💡 Hint

Common Mistakes

Using %f or %c instead of %d for integers.

Forgetting to use & before variable names in scanf.

The scanf format specifier "%d %d" reads two integers from input.

2fill in blank

medium

Complete the code to print two floating-point numbers with two decimal places.

C

#include <stdio.h>

int main() {
    float x = 3.1415, y = 2.7182;
    printf([1], x, y);
    return 0;
}

Drag options to blanks, or click blank then click option'

A"%c %c\n"

B"%d %d\n"

C"%.2f %.2f\n"

D"%f %f\n"

Attempts:

3 left

💡 Hint

Common Mistakes

Using %d to print floats.

Not specifying decimal places, leading to many decimals.

The format "%.2f" prints a floating-point number with two digits after the decimal point.

3fill in blank

hard

Fix the error in the code to correctly read a character and an integer.

C

#include <stdio.h>

int main() {
    char c;
    int n;
    printf("Enter a character and a number: ");
    scanf("%c [1]", &c, &n);
    printf("You entered %c and %d\n", c, n);
    return 0;
}

Drag options to blanks, or click blank then click option'

A%f

B%d

C%c

D%s

Attempts:

3 left

💡 Hint

Common Mistakes

Using %c twice in scanf.

Using %f or %s for integers.

After reading a character with %c, use %d to read an integer.

4fill in blank

hard

Fill both blanks to read and print two integers separated by a space.

C

#include <stdio.h>

int main() {
    int a, b;
    printf("Enter two integers: ");
    scanf([1], &a, &b);
    printf([2], a, b);
    return 0;
}

Drag options to blanks, or click blank then click option'

A"%d %d"

B"%f %f"

C"%d %d\n"

D"%c %c"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong format specifiers in scanf or printf.

Forgetting newline in printf.

Use "%d %d" to read two integers and "%d %d\n" to print them with a newline.

5fill in blank

hard

Fill all three blanks to read a character, an integer, and a float, then print them.

C

#include <stdio.h>

int main() {
    char ch;
    int num;
    float val;
    printf("Enter a character, an integer, and a float: ");
    scanf([1], &ch, &num, &val);
    printf([2], ch, num, val);
    return [3];
}

Drag options to blanks, or click blank then click option'

A"%c %d %f"

B"%c %d %f\n"

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up format specifiers.

Forgetting newline in printf.

Returning 1 instead of 0.

Use "%c %d %f" to read char, int, float; "%c %d %f\n" to print them; return 0 to end program.

Practice

1. What does the following C code do?
int a, b;
scanf("%d %d", &a, &b);
printf("%d %d", a, b);

easy

A. Prints two integers without reading input.

B. Reads one integer and prints it twice.

C. Reads two integers from input and prints them in the same order.

D. Reads two integers but prints only the first one.

Solution

1. Step 1: Understand scanf with multiple inputs

   The scanf function reads two integers from the user input and stores them in variables a and b.

2. Step 2: Understand printf with multiple outputs

   The printf function prints the values of a and b in the same order they were read.

3. Final Answer:

   Reads two integers from input and prints them in the same order. -> Option C

4. Quick Check:

   scanf and printf with two %d = same two integers [OK]

Hint: Match each %d with a variable and & in scanf [OK]

Common Mistakes:

• Forgetting & before variables in scanf
• Mixing order of variables in printf
• Using wrong format specifiers

2. Which of the following is the correct syntax to read three integers a, b, c in C?

easy

A. scanf("%d %d %d", &a, &b, &c);

B. scanf("%d %d %d", a, b, c);

C. scanf("%d, %d, %d", &a, &b, &c);

D. scanf("%d %d %d", *a, *b, *c);

Solution

1. Step 1: Check scanf format string and arguments

   The format string should have three %d separated by spaces, and variables must be passed by address using &.

2. Step 2: Identify correct option

   scanf("%d %d %d", &a, &b, &c); uses correct format string and & before variables, so it is correct.

3. Final Answer:

   scanf("%d %d %d", &a, &b, &c); -> Option A

4. Quick Check:

   Use & with variables in scanf [OK]

Hint: Always use & before variables in scanf [OK]

Common Mistakes:

• Omitting & before variables
• Using commas inside format string incorrectly
• Using pointers incorrectly with *

3. What is the output of this C program?

int x, y;
scanf("%d %d", &x, &y);
printf("%d %d %d", x, y, x + y);

Input:
3 7

medium

A. 10 10 20

B. 3 7 10

C. 7 3 10

D. 3 7 37

Solution

1. Step 1: Read input values

   scanf reads 3 into x and 7 into y.

2. Step 2: Calculate and print output

   printf prints x (3), y (7), and x + y (3 + 7 = 10).

3. Final Answer:

   3 7 10 -> Option B

4. Quick Check:

   3 + 7 = 10 [OK]

Hint: Add variables inside printf for combined output [OK]

Common Mistakes:

• Mixing order of variables in printf
• Confusing concatenation with addition
• Not using & in scanf

4. Find the error in this code snippet:

int a, b;
scanf("%d %d", a, b);
printf("%d %d", a, b);

medium

A. Missing semicolon after scanf.

B. Wrong format specifier in scanf.

C. printf format specifiers do not match variables.

D. Missing & before variables in scanf.

Solution

1. Step 1: Check scanf arguments

   scanf requires addresses of variables, so &a and &b are needed.

2. Step 2: Identify error

   Code passes variables a and b directly, causing undefined behavior or crash.

3. Final Answer:

   Missing & before variables in scanf. -> Option D

4. Quick Check:

   scanf needs & before variables [OK]

Hint: Always use & before variables in scanf [OK]

Common Mistakes:

• Forgetting & in scanf
• Assuming variables auto-pass by address
• Confusing scanf and printf syntax

5. Write a C program snippet that reads two integers and prints their sum and product separated by a space. Which code correctly does this?

hard

A. int a, b;scanf("%d %d", &a, &b);printf("%d %d", a + b, a * b);

B. int a, b;scanf("%d %d", a, b);printf("%d %d", a + b, a * b);

C. int a, b;scanf("%d %d", &a, &b);printf("%d %d", a - b, a / b);

D. int a, b;scanf("%d %d", &a, &b);printf("%d %d", a * b, a + b);

Solution

1. Step 1: Check input reading correctness

   scanf must use &a and &b to read two integers correctly.

2. Step 2: Check output matches sum and product

   printf should print sum (a + b) first, then product (a * b) separated by space.

3. Final Answer:

   int a, b; scanf("%d %d", &a, &b); printf("%d %d", a + b, a * b); -> Option A

4. Quick Check:

   scanf with & and printf sum then product [OK]

Hint: Print sum first, product second with correct scanf [OK]

Common Mistakes:

• Forgetting & in scanf
• Swapping sum and product order
• Using wrong operators in printf