String input and output in C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What function is commonly used in C to read a string from the user?

The scanf function is commonly used to read strings from the user in C, often with the format specifier %s.

beginner

How do you print a string stored in a variable in C?

Use the printf function with the format specifier %s to print a string variable, for example: printf("%s", str);

intermediate

What is a safe way to read a string input to avoid buffer overflow?

Use fgets instead of scanf to read strings safely by specifying the maximum number of characters to read, e.g., fgets(str, sizeof(str), stdin);

intermediate

What happens if you use scanf("%s", str); and the input is longer than the buffer?

It causes a buffer overflow, which can overwrite memory and lead to crashes or security issues because scanf does not limit input length.

beginner

How do you declare a string variable in C?

A string in C is an array of characters ending with a null character \0. For example: char str[100]; declares a string that can hold up to 99 characters plus the null terminator.

Which function is safer to read a string input in C?

A fgets

B scanf with %s

C gets

D printf

fgets is safer because it limits the number of characters read, preventing buffer overflow. gets is unsafe and deprecated. scanf with %s does not limit input size.

What format specifier is used to print a string in C?

A %d

B %s

C %f

D %c

The %s format specifier is used with printf to print strings.

What does the null character \0 signify in a C string?

A Space character

B Start of the string

C End of the string

D New line

The null character \0 marks the end of a string in C.

Which of these is a correct way to declare a string that can hold 50 characters?

A char str;

B int str[50];

C string str;

D char str[51];

Strings in C are arrays of characters, so char str[51]; declares a string with space for 50 characters plus the null terminator.

What is the risk of using scanf("%s", str); without limiting input size?

A Buffer overflow

B Syntax error

C No risk

D Memory leak

Using scanf without limiting input size can cause buffer overflow, which may crash the program or cause security issues.

Explain how to safely read and print a string in C.

Think about how to avoid buffer overflow and how strings end in C.

Describe the difference between using scanf and fgets for string input in C.

Consider safety and how input is stored.