Syntax of command line arguments - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are command line arguments in C?

Command line arguments are inputs passed to a C program when it starts. They allow users to provide data or options to the program from the terminal or command prompt.

beginner

What is the syntax of the main function to accept command line arguments in C?

The main function should be declared as int main(int argc, char *argv[]) or int main(int argc, char **argv). Here, argc counts the arguments, and argv is an array of strings holding each argument.

beginner

What does argc represent in the main function?

argc stands for 'argument count'. It tells how many command line arguments were passed, including the program's name itself.

beginner

What is stored in argv[0]?

argv[0] stores the name or path of the program being executed. It is always the first argument.

beginner

How can you access the third command line argument in a C program?

You can access it using argv[3]. Remember, argv[0] is the program name, so the first user argument is argv[1].

What is the correct declaration of main to accept command line arguments?

A void main()

B int main(int argc, char *argv[])

C int main()

D void main(int argc)

Only int main(int argc, char *argv[]) correctly accepts command line arguments.

What does argc count?

A Number of user arguments excluding program name

B Number of characters in the first argument

C Number of bytes in argv array

D Number of command line arguments including program name

argc counts all arguments including the program name.

What is stored in argv[0]?

A Program name or path

B First user argument

C Last argument

D Null pointer

argv[0] always holds the program's name or path.

If a program is run as ./app hello world, what is argv[2]?

A NULL

B hello

C world

D ./app

argv[0] is './app', argv[1] is 'hello', and argv[2] is 'world'.

Which data type is argv in int main(int argc, char *argv[])?

A Array of pointers to char

B Pointer to int

C Array of integers

D Pointer to float

argv is an array of pointers to characters (strings).

Explain the purpose and syntax of command line arguments in C programs.

Think about how you run programs from the terminal with extra words.

Describe how to access the first and second user-provided command line arguments in C.

Remember the program name is always the first argument.

Practice

1.

What does the argc parameter represent in a C program's main function?

easy

A. The number of command line arguments including the program name

B. The array of command line argument strings

C. The first command line argument

D. The program's exit status

Solution

1. Step 1: Understand the role of argc

   argc stands for 'argument count' and tells how many arguments are passed to the program including the program name itself.

2. Step 2: Differentiate argc from argv

   argv is the array holding the actual argument strings, not the count.

3. Final Answer:

   The number of command line arguments including the program name -> Option A

4. Quick Check:

   argc = argument count [OK]

Hint: Remember: argc counts all arguments including program name [OK]

Common Mistakes:

• Confusing argc with argv
• Thinking argc excludes the program name
• Assuming argc is the argument array

2.

Which of the following is the correct syntax for the main function to accept command line arguments in C?

easy

A. int main(char argc, char *argv[])

B. void main()

C. int main(int argc, char *argv[])

D. int main(int argv, char *argc[])

Solution

1. Step 1: Recall the standard signature for main with arguments

   The correct signature uses int argc and char *argv[] to receive argument count and argument strings.

2. Step 2: Identify incorrect options

   void main() lacks parameters, C uses wrong type for argc, D swaps argc and argv incorrectly.

3. Final Answer:

   int main(int argc, char *argv[]) -> Option C

4. Quick Check:

   Main signature with argc and argv = int main(int argc, char *argv[]) [OK]

Hint: argc is int, argv is array of char pointers [OK]

Common Mistakes:

• Using void main instead of int main
• Swapping argc and argv types
• Using char type for argc

3.

What will be the output of the following C program if run as ./program hello world?

int main(int argc, char *argv[]) {
    printf("%d %s %s", argc, argv[1], argv[2]);
    return 0;
}

medium

A. 3 hello world

B. 2 hello world

C. 3 ./program hello

D. Error: argv[2] does not exist

Solution

1. Step 1: Count the arguments passed

   Running ./program hello world passes three arguments: program name, "hello", and "world". So, argc = 3.

2. Step 2: Identify argv values

   argv[0] = "./program", argv[1] = "hello", argv[2] = "world".

3. Final Answer:

   3 hello world -> Option A

4. Quick Check:

   argc=3, argv[1]=hello, argv[2]=world [OK]

Hint: argv[0] is program name; argc counts all args [OK]

Common Mistakes:

• Assuming argc excludes program name
• Confusing argv indexes
• Thinking argv[2] is out of range

4.

Identify the error in this C program snippet that uses command line arguments:

int main(int argc, char *argv[]) {
    printf("%s", argv[argc]);
    return 0;
}

medium

A. argc should be a char type

B. Accessing argv[argc] causes out-of-bounds error

C. argv should be int array

D. Missing return statement

Solution

1. Step 1: Understand argv indexing

   argv indexes go from 0 to argc-1. Accessing argv[argc] is out of bounds and unsafe.

2. Step 2: Check other options

   argc must be int, argv is array of char pointers, and return statement is present.

3. Final Answer:

   Accessing argv[argc] causes out-of-bounds error -> Option B

4. Quick Check:

   argv valid indexes: 0 to argc-1 [OK]

Hint: argv max index is argc-1, not argc [OK]

Common Mistakes:

• Using argv[argc] instead of argv[argc-1]
• Changing argc type incorrectly
• Ignoring array bounds

5.

How would you write a C program that prints all command line arguments except the program name, each on a new line?

hard

A. Print argc without looping

B. Print argv[0] only

C. Use a loop from 0 to argc and print argv[i]

D. Use a loop from 1 to argc-1 and print argv[i]

Solution

1. Step 1: Understand argument indexing

   argv[0] is the program name, so to print only arguments, start from index 1.

2. Step 2: Loop through arguments

   Loop from i=1 to i<argc to print each argument on a new line.

3. Final Answer:

   Use a loop from 1 to argc-1 and print argv[i] -> Option D

4. Quick Check:

   Skip argv[0], loop i=1 to argc-1 [OK]

Hint: Start loop at 1 to skip program name [OK]

Common Mistakes:

• Starting loop at 0 printing program name
• Looping beyond argc-1 causing errors
• Not using a loop to print all arguments