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C Programming

1.2 Python to C

To learn C from a Python background, here are key steps to help you transition:

  • Understand Syntax Differences:

    • C is statically typed (you need to declare variable types), while Python is dynamically typed.
    • Example: 
      int x = 10;

  • Memory Management:

    • C requires manual memory management using malloc() and free() for dynamic memory allocation, while Python handles this automatically.

  • Pointers:

    • C uses pointers to reference memory locations. Grasp how to use pointers and understand pointer arithmetic.

  • Functions and Libraries:

    • C standard libraries like <stdio.h> and <stdlib.h> are used for I/O and memory management. Functions need explicit return types and argument declarations.

  • Build Process:

    • C requires compiling with a compiler like gcc, while Python is interpreted. Learn to compile, link, and execute C code.

  • Debugging:

    • Unlike Python, C can lead to segmentation faults due to memory misuse. Learn to use debugging tools like gdb or valgrind.

  • Practical Projects:

    • Start with simple programs like basic calculators, file I/O operations, and eventually implement data structures.

  • Resources:

    • Books like “The C Programming Language” by Kernighan and Ritchie.
    • Online platforms like Learn-C.org or Exercism.

1. Hello World

Python C
def func ()
    print ("Hello World!")
void func ()
{
    printf ("Hello World!\n");
}

2. Use of Semicolon ;

The semicolon (;) is treated differently in Python and C:

In C:

  • Semicolon is required to terminate statements: Each statement in C must end with a semicolon to indicate the end of the command.

    Example:

    int x = 5;  // Semicolon required
    printf("%d\n", x);  // Semicolon required

    Without a semicolon, the compiler throws an error.

In Python:

  • No semicolons are required: Python uses newlines and indentation to define the end of a statement or block of code. Semicolons are optional but rarely used.

    Example:

    x = 5  # No semicolon needed
    print(x)  # No semicolon needed

  • Optional use: You can use semicolons to write multiple statements on a single line, but this is not typical Python style.

    Example:

    x = 5; print(x)  # Multiple statements on one line using a semicolon

3. User Input

Python C
def userInput ():


  # Integer input
  var_int = int(input ())


  # Double ( real number )
  var_dbl = float(input())


  # String
  var_str = input ()
void userInput ()
{
  int var_int;
  double var_dbl;
  char var_str [101];


  /* String with max length of
  100 characters */
  /* Integer */
  scanf ("%d", &var_int );


  /* Double */
  scanf ("%f", &var_dbl );


  /* String */
  scanf ("%s", var_str );


  /* `&` is not needed
  since `var_str` an array */
}

3.1 Control Structures

Control structures are constructs in programming that dictate the flow of execution based on conditions, loops, and decision-making. They help manage how and when specific parts of the code are executed.

3.1.1 If Statement

  • Python: Uses indentation to define code blocks.
  • C: Uses braces {} to group code blocks
Python C
def func (a):


  if a == 10:
    print ("It is 10")


  elif a > 10:
    print (" Greater than 10")


  else :
    print ("Not high enough")
void func (int a)
{
  if(a == 10)
  {
    printf ("It is 10");
  }
  else if(a > 10)
  {
    printf (" Greater than 10");
  }
  else
  {
    printf ("Not high enough ");
  }
}

3.1.2 For Loop

  • Python: Uses for item in range().
  • C: Uses initialization, condition, and increment in a more explicit form.
Python C
def func ():
  # 0 -10 Inclusive
  for i in range (11):
    print (i)
void func ()
{
  /* 0 -10 Inclusive */
  int i;
  for (i = 0; i < 11; i++)
  {
    printf ("%d\n", i);
  }
}

3.1.3 While Loop

  • Both languages use while, but C requires braces {} for blocks.
Python C
def func ():
  var = 0
  while var >= 0:
    print ("Enter value")
    var = int(input())
void func ()
{
  int var = 0;
  while ( var >= 0)
  {
    printf ("Enter value\n");
    scanf ("%d", &var);
  }
}

3.1.4 Swtich Statement

  • C: Includes switch-case for multi-branch decision-making, which Python doesn’t have directly.
Python C
# Note that python has no actual switch statement
def func ( grade ):
  if grade == 'A':
    print ("Excellent")


  elif grade == 'B' or
    grade == 'C':
    print ("Well Done")


  elif grade == 'D':
    print ("You Passed")


  elif grade == 'F':
    print ("Try again")


  else :
    print ("Invalid Grade")
void func (char grade)
{
  switch (grade)
  {
  case 'A':
    printf ("Excellent");
    break ;


  case 'B' : case 'C':
    printf ("Well Done");
    break ;


  case 'D':
    printf ("You Passed");
    break ;


  case 'F':
    printf ("Try again");
    break ;


  default :
    print ("Invalid Grade")
  }
}

3.1.5 Ternary Operator

  • Python: Uses conditional expressions, which are more readable but serve a similar purpose.
  • C: Supports the ternary operator ? :, a shorthand for if-else.
Python C
y = 10 if x > 5 else 0
int y = (x > 5) ? 10 : 0;

3.2 Function Calls

3.2.1 Main Function

Python C
if __name__ == " __main__ ":


  print ("Argument Count:",
  len(sys . argv ))


  print ("Arguments:\n")
  for arg in sys . argv :
    print (arg)
int main (int argc , char * argv [])
{
  int i;
  printf ("Argument Count: %d\n",
  argc );


  printf ("Arguments:\n");
  for (i = 0; i < argc ; i ++)
  {
    printf ("%s\n", argv [i]);
  }


  return 0;
}

3.2.2 Returning Values

Python C
def func3(x):
  # Do something
  pass


def func2():
  return 5


def func1():
  a = func2()
  func3(a)
void func3(int x)
{
  /* Do something */
}


int func2()
{
  return 5;
}


void func1()
{
  int a = func2();
  func3(a);
}