Using scanf for input - Cheat Sheet & Quick Revision

Recall & Review

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What is the purpose of scanf in C?

scanf is used to read input from the user through the keyboard and store it in variables.

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How do you read an integer value using scanf?

Use scanf("%d", &variable); where variable is an int type.

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Why do we use the ampersand (&) before the variable name in scanf?

The ampersand & gives the memory address of the variable so scanf can store the input value there.

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What format specifier is used to read a floating-point number with scanf?

Use %f to read a float value.

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How can you read a string (word) using scanf?

Use scanf("%s", variable); where variable is a character array (e.g., char name[20];).

Which of the following is the correct way to read an integer using scanf?

A scanf("%d", num);

B scanf("%d", &num);

C scanf("%i", num);

D scanf("int", &num);

Option B correctly uses the format specifier %d and the address operator &.

What does scanf return after reading input?

A The number of input items successfully matched and assigned

B The input value itself

C The memory address of the variable

D Nothing (void)

scanf returns how many inputs it successfully read and stored.

Which format specifier reads a floating-point number in scanf?

A %f

B %d

C %c

D %s

%f is used for reading float values.

How do you read a single character using scanf?

A scanf("char", ch);

B scanf("%s", &ch);

C scanf("%d", &ch);

D scanf("%c", &ch);

%c reads a single character and requires the address of the variable.

Why might scanf("%s", name); be unsafe without precautions?

A It reads only one character

B It does not store the input

C It can cause buffer overflow if input is longer than the array size

D It requires an ampersand (&) before the variable

Without limiting input size, scanf can overflow the buffer causing errors.

Explain how to use scanf to read an integer and why the ampersand (&) is needed.

Think about how scanf needs to know where to put the input value.

Describe the risks of using scanf to read strings and how to avoid them.

Consider what happens if user types more characters than the array can hold.