Using scanf for input - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Reading an integer with scanf

What is the output of this C program when the user inputs 42?

C

#include <stdio.h>

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    printf("You entered: %d\n", num);
    return 0;
}

A You entered: 42

B Compilation error

C You entered: %d

D You entered: 0

💡 Hint

Remember scanf needs the address of the variable to store the input.

The scanf function reads the integer input 42 and stores it in the variable num. Then printf prints it correctly.

❓ Predict Output

intermediate

Reading multiple inputs with scanf

What will be printed if the user inputs 10 20?

C

#include <stdio.h>

int main() {
    int a, b;
    scanf("%d %d", &a, &b);
    printf("Sum: %d\n", a + b);
    return 0;
}

A Sum: 30

B Sum: 1020

C Sum: 10

D Runtime error

💡 Hint

scanf reads each integer separately when given multiple format specifiers.

scanf reads two integers 10 and 20, stores them in a and b, then prints their sum 30.

❓ Predict Output

advanced

Using scanf with wrong format specifier

What happens when this program runs and the user inputs 3.14?

C

#include <stdio.h>

int main() {
    int x;
    scanf("%d", &x);
    printf("Value: %d\n", x);
    return 0;
}

A Runtime error

B Value: 0

C Value: 3.14

D Value: 3

💡 Hint

scanf with %d reads integer part and stops at decimal point.

scanf with %d reads integer part 3 from input 3.14 and stores it in x. The decimal part is ignored.

❓ Predict Output

advanced

Reading a string with scanf

What will be the output if the user inputs HelloWorld?

C

#include <stdio.h>

int main() {
    char str[20];
    scanf("%s", str);
    printf("You typed: %s\n", str);
    return 0;
}

A You typed: Hello World

B You typed: HelloWorld

C You typed: HelloWorld\n

D Buffer overflow error

💡 Hint

scanf with %s reads input until first whitespace.

scanf reads the string HelloWorld into str and prints it exactly.

❓ Predict Output

expert

Using scanf with character input and newline

What will be printed if the user inputs A and presses Enter?

C

#include <stdio.h>

int main() {
    char c1, c2;
    scanf("%c", &c1);
    scanf("%c", &c2);
    printf("Chars: %c and %c\n", c1, c2);
    return 0;
}

A Chars: A and (space)

B Chars: A and A

C Chars: A and \n

D Runtime error

💡 Hint

The second scanf reads the leftover newline character from input buffer.

First scanf reads 'A', second scanf reads the newline character '\n' left in the input buffer.