What will be the output of the following C code?

char str[20]; 
strcpy(str, "123456"); 
res = atoi(str);
printf("%s  %d\n", str, res);

Which standard library function is used to calculate the length of a string in C?

A. strlen()

B. strlength()

C. stringlen()

D. strsize()

What is the purpose of the 'printf' function in C?

A. To print formatted text to the standard output

B. To read text from the standard input

C. To open a file

D. To close a file

Which library should be included to use the 'sqrt' function in C?

A. math.h

B. stdlib.h

C. cmath.h

D. algorithm.h

What does the 'strcmp' function in C do?

A. Compares two strings and returns an integer indicating their relationship

B. Copies one string to another

C. Concatenates two strings

D. Searches for a substring