Introduction to C language

Introduction to C


     C is a general purpose programming language. Programming language is the means to communicate with the system to get our thing done.

Need for a programming language:

  We all of us know system can only understand binary representation i.e. in the form of 0's and 1's.

Suppose we have to program which adds two numbers and save the result.

Steps involved:
  • First we should write the values in the memory.
  • Move those values into the registers.(registers are also a kind of memory where the CPU can perform operation on the values stored in the registers.)
  • Add the values in the registers.
  • Save the result in the register to the memory.

Machine Language                                                                                                                                                                                                                                                                               At the beginning machine code is used to write the program. 

Machine level programming consists of binary or hexadecimal instructions on which an processor can respond directly.  

Structure of machine language instruction.
Opcode   Operand 

Opcode represents the operation to be performed by the system on the operands.

In machine code:
Memory     opcode     operand 
location                                                                     
0000:           55            e4     10   // 55 represent move instruction, move 10 to location e4          
0001:           89            e5     20
0003:           83            e4     e5
0006:           54            c4     e4    

Its difficult to read and write opcode for every instruction. So instead of numerical value for instruction there should be an alternative, Then comes the assembly code.

Assembly language:

 Mnemonics are used to represent the opcode.
An Assembly code:
MOV  A, $20           // move value 20 to register A (MOV is a mnemonics)
MOV  B, $10           // move value 10 to register B
ADD   A, B              // Add value in register in A and B
MOV  #30, A           // move value in register A to address 30

Assemblers converts the assembly language into binary instructions.
Assembly language is referred to as low level language,
Assembler languages are simpler than opcodes. Their syntax is easier to read than machine language but as the harder to remember. So, their is a need for other language which is much more easy to read and write the code.
Then comes the C programming language.

C language

In C language:
 int main()
{
     int a,b,c;
     a=10;
     b=20;
     c=a+b;
}

Compiler converts the C language code into assembly language code.

C language is easier to write and read. 

Factorial program in python

#write a python program for factorial of a given number.

num = int(input("Enter a number: "))
factorial = 1
if num < 0:
   print("factorial not exist for negative numbers")
elif num == 0:
   print("The factorial of 0 is 1")
else:
   for i in range(1,num + 1):
       factorial = factorial*i
   print("The factorial of",num,"is",factorial)

  • We store the number we give in the num variable and by using the if, elif, and else loop we are executing the program. if statement executes when the given condition is true and same for elif also. After the iteration, it finally returns the factorial of the number we are given.
  • Normally we write as 12!=12*11*10*9*8*7*6*5*4*3*2*1=479001600




find substring python

 find substring():

  • The find substring is used to find the substring from the string.
  • Substring is the piece of characters from the string.
  • If the string consists of the given string then it returns the index number of the substring. 
  • The string must be enclosed with single or double-quotes.
  • It returns -1 if the substring does not found instead of an error.
  • find() has 3 parameters,they are:
  1. value: The value to be search
  2. start:  from where to search
  3. end:  from where to stop searching.
Syntax: str.find(value,start,end)

#write a python code to demonstrate the find substring function.

  1. txt="learning is a life time process"
  2. txt=txt.find("i")
  3. print(txt)
  4. s="apple"
  5. s=s.find("b")
  6. print(s)

Output: 5
              -1







python replaceall

  • In python, replace all is similar to replace() function. 
  • Here we are going to replace all the characters with new characters.
  • It also consists of 3 parameters like new value, old value, count.
  • The old value is the string that we have already given in string.
  • The new value is the that is to be replaced with.
  • The count is the number of times that string to be replaced in the string.
Syntax:  str.replace(old value,new value,count)

#write a python code to demonstrate the replace function.

  1. s="hello world"
  2. s=s.replace("hello world","my name is hello")
  3. print(s)
Output:    my name is hello


format function in python

  •  The format() function is used to format a specific value and insert that value in string placeholders.
  •  The placeholders are cost{20}, number index{1},empty{}
  • The place holder is defined by" curly braces"{}.
  • The format function consists of parameters called value.
  • It returns the formatted string.
Syntax:  str.format(values)

  • Inside the placeholders, we can add different formatting types
  • :+    indicates positive values.
  • : -    indicates negative values.
  • :      indicates the space before positive and also negative numbers.
  • :_    indicates as a thousand separator.
  • :,     uses as comma thousand separator.
  • :=    left most position.
  • :<    result in left alignment.
  • :>    result in right alignment.
  • :^     result in the center.
  • :%    percentage format.
  • :b     Binary format.
  • :c     Unicode format.
  • :d     Decimal format.
  • :e      format with lower case.
  • :E     format with upper case.
  • :f      format with fixpoint number.
  • :o    format is octal.
  • :x      format is Hexa.
  • :X     format is Hexa in uppercase.
  • :n      number format.

#write a python code to demonstrate format function.

  1. s0="my name is {fname},I m {age}".format("fname=abc",age=19)
  2. s1="my name is{0},I m {1}".format("abc",19)
  3. s2="my name is {},I m {}".format("abc",19)
  4. print(s0)
  5. print(s1)
  6. print(s2)

Output:    my name is abc, I m 19.
                 my name is abc, I m 19.
                 my name is abc, I m 19.


string reverse in python

  • The reverse string in python is not an in-built function.
  • By creating the slice operation we can perform the reverse function.
  • In this slice operation, we create the slice that starts with the end of the string and moves backward.
  • String reverse in python example program
Example: " abcdefg"[::-1]

                     gfedcba

 right to left indexing:              [-7]    [-6]    [-5]    [-4]      [-3]     [-2]      [-1]

                                                    a          b      c        d          e          f         g 

left to right indexing:             [0]         [1]     [2]     [3]     [4]       [5]        [6]

  • In the above example, we are having the string  "abcdefg " which we want to reverse. so create a slice that starts with the end of the string and moves backward.
  • here it starts with the end index that is indicated with -1 and moves backward as 5,4,3,2,1,0.
  • -1 index  is g
  • 5 index is f
  • 4 index is e
  • 3 index is d
  • 2 index is c
  • 1 index is b
  • 0 index is a
  • so the final output is gfedcba.

#write a python code to demonstrate string reverse.

  1. txt="today climate is very cool"[::-1]
  2. txt1="hello world"[::-1]
  3. print(txt)
  4. print(txt1)
Output:    looc yrev si etamilc yadot
                  dlrow olleh


python tolower

  •  In python, to lower is used to convert the uppercase letters to lower case.
  • It uses the function called lower().
  • It doesn't have any parameters.
  • The string must be enclosed with single or double-quotes.
  • If the string does not contain any upper case letters then it returns the same string.
Syntax: str.lower()

Example: s="HELLO"

             str.lower(s)=hello

#write a python code to demonstrate the lower() function.

  1. s="APPLE IS A FRUIT"
  2. print(str.lower(s))
  3. x="My NAme IS  aBCba"
  4. print(str.lower(x))
output: apple is a fruit
              my name is abcba


remove spaces from string python

  •  In python, we have different functions which remove the spaces between the strings.
  • There are three functions that remove the whitespace between the strings, they are:
  • strip(), rstrip(), lstrip()  are the three functions having the same meaning but some differences.
strip(): It removes the whitespace at the beginning and end.

syntax: str.strip()

lstrip(): It removes the whitespace at beginning of the string.

syntax: str.rstrip()

rstrip(): It removes the whitespace at end of the string.

syntax: str.rstrip()

Example: write a python to demonstrate the remove space function.

  1. txt="    hello"
  2. print(txt)
  3. print(txt.strip())
  4. print(txt.rstrip())
  5. print(txt.lstrip())
Output:         hello    //this is the original output
                  hello         //after removing both side space
                     hello      //no space at  end returns same 
                hello          //remove space at the beginning.


replace function in python

 replace function:

python having different types of in-built functions from them replace() is one of the function.
  • The replace() function name itself saying that "one string is replaced with the other string".
  • It consists of three parameters old value, new value, and count.
old value:  The value that we want to replace.

new value: The value we want to replace with is the new value.

count: The number of times of the value we want to replace old with the new value.

Syntax: str.replace(old value,new value,count)

#write a python code to demonstrate replace function.

  1. a="my name is java"
  2. b=" she is a very talented person"
  3. c="They have no knowledge in python"
  4. a=a.replace("java","python")
  5. b=b.replace("talented person","brave girl")
  6. c=c.replace("no","more",3)
  7. print(a)
  8. print(b)
  9. print(c)
  • In the above program in line 5, we want to replace no with more and we gave the count as 3 so in the string where we have no that will be replaced with more up to 3 times only.
  • so the output will be as shown in below.
Output:  my name is python
               she is a very brave girl
              They have more kmorewledge in python 



strip function in python


In Python, the str.strip() method is used to remove leading and trailing whitespaces from a string. By default, the strip() method removes any whitespace characters from the beginning and end of the string, such as spaces, tabs, and newlines. 
The strip() function is a string method that removes leading and trailing whitespace characters from a string. By default, it removes spaces, tabs, and newline characters from the beginning and end of a string. 
However, it can also be used to remove any specified characters from the beginning and end of a string.
Here's an example of strip() method:

It's important to note that the strip() function returns a new string and does not modify the original string.
We can also use lstrip() and rstrip() to remove leading and trailing whitespaces respectively.
strip() function in Python is a useful method for removing unwanted characters from the beginning and end of a string, which helps in cleaning up the data and making it ready for further processing or analysis.

original_string = "   Hello World   "
stripped_string = original_string.strip()
print(stripped_string)

This will print "Hello World" with leading and trailing whitespaces removed.

In addition to removing whitespaces, the strip() method can also remove specific characters from the beginning and end of the string. You can pass one or more characters as arguments to the strip() method, and it will remove those characters from the beginning and end of the string. Here's an example:


original_string = "!!Hello World!!"
stripped_string = original_string.strip('!')
print(stripped_string)

This will print "Hello World" with the leading and trailing '!' characters removed.

Alternatively, you can use lstrip() and rstrip() method to remove leading and trailing whitespaces respectively.


original_string = "   Hello World   "
stripped_string = original_string.lstrip()
print(stripped_string)

This will print "Hello World " with leading whitespaces removed.


original_string = "   Hello World   "
stripped_string = original_string.rstrip()
print(stripped_string)

This will print " Hello World" with trailing whitespaces removed.

It's worth noting that, the strip() method returns a new string with the leading and trailing whitespaces removed, it does not modify the original string.
  • In python, we are having another in-built function called "strip()".
  • The strip() function is used to remove the spaces of the starting and end of the string.
  • It is having one parameter character used to remove the begging or end character.
  • By default, it removes the white spaces at the beginning or end.
  • If there is no white space between the beginning or end, the string remains the same and returns the same string.
  • When the character we give does not match the start or end, it returns the same string.
  • If the character is given at start to remove then the space will be removed and the remaining will remain the same.
syntax: str. strip(char)

#write a python program to demonstrate the strip function()

  1. txt1="   my name is python"
  2. txt2="***my name is python***"
  3. txt3=",,,my name is python"
  4. txt1=txt1.strip()
  5. txt2=txt2.strip("*")
  6. txt3=txt3.strip(".")
  7. print(txt1)
  8. print(txt2)
  9. print(txt3)
Output: my name is python
               my name is python
               my name is python

length of string python

 length of the string:

  • The len() function gives the length of the string.
  • As it returns the result in integer type.
  • It takes the string as the parameter.
  • We can use len() for list,tuple,set,dictionry.
  • The len() is the built-in function in python programming.
  • Example:  "string"  its length is  6.
Syntax: str(length)

#write a python program to demonstrate the length of the string.

  1. string="america"
  2. print(len(string))
Output: 7


concat python

 concatenation:

  • In python, concatenation is defined as "the process of combining or joining or merging one string with the other string".
  •  It uses the plus operator for combining the strings.
  • The string must be enclosed with single quotations or double.
  • Type conversion is needed.
  • We can combine an integer value with a string by using the str(int) function.
  • The plus(+) operator is used to combine the string at the end of the string.
  • The % string format operator is used to combine the string anywhere we want.
Syntax: str1+str2

#write a python program to demonstrate concatenation function.

  1. a="python"
  2. b="programming"
  3. x=a+b
  4. print(x)
  5. str1="python"
  6. str2=str(3.0)
  7. str=str1+str2
  8. print(str)
Output: pythonprogramming
              python3.0



startswith python

  •  In python, we have another built-in method called startswith.
  • startswith is used to check whether the string startswith this specified string.
  • It returns the boolean type.
  • If the string startswith gave specified string then it returns true else false.
Syntax: str.startswith(value,start,end)

  • It consists of the 3 parameters.
  1. value:  The value that the string starts with.
  2. start:    The position to start the search of string.
  3. end:  The position to end the search.

#write a python program to demonstrate the startswith method.

  1. str="welcome to python"
  2. str=str.startswith("w",0,14)
  3. print(str)
Output:true

strftime python

 strftime :

  •  The method represents the string consists of data and time with objects as time and date or date time.
  • The datetime class is imported from the date time module.
  • It takes one or more input format codes and returns string representation.
Syntax: strftime(format)

  • The list of format codes are:
  1. %a:  It is used for weekdays representation in short forms as wed, thr, etc...
  2. %A: It is used for weekdays representation in the full name as of Sunday, Monday.
  3. %b: It is used for month name representation in short form as of Jan, Feb, etc
  4. %B: It is used for month name representation in the full name as of April, May, etc.
  5. %d: It is used as a representation of the day of the month as zero added.
  6.  %-d: day of the month as a decimal number.
  7. %m: Month as zero added decimal number. 
  8. %-m: Month as a decimal number.
  9. %H:  hours as zero added decimal number.
  10. %-H: hours as a decimal number.
  11. %M: minutes as zero added decimal number.
  12. %-M: minutes as a decimal number.
  13. %S: seconds as a zero added decimal number
  14. %-S: seconds as a decimal number.
  15. %J: day of the year as zero added decimal number.
  16. %-J: day of the year as a decimal number.

#write a python program to demonstrate strftime function.

  1. from datetime import datetime
  2. now=datetime.now()
  3. year=now.strftime("%Y")
  4. print("year:",year)
  5. month=now.strftime("%m")
  6. print("month:",month)
  7. day=now.strftime("%d")
  8. print("day:",day)
  9. time=now.strftime("%H:%M:%S")
  10. print("time:",time)
  11. date_time=now.strftime("%m%d%Y, %H%M%S")
  12. print("date and time:",date_time)
output:
year:2021
month:07
day:05
time:10:50:36
date and time:07052021,105036



is numeric python

is numeric:

  •  Is numeric is the built-in method that is used to check whether the string contains numbers or not.
  • It returns the true when the string contains numbers, if the string does not contain numbers then it returns false.
  • It is applicable for integers, Unicode values. and takes the exponents like 1/2.
  • It is not applicable for float and negative values.
  •  isnumeric does not have any parameters.
  • For negative values to check whether they are numeric or not we have to remove the negative sign.
syntax:  str.isnumeric()

Example: a="12345"

                 a=str.isnumeric(a)

                 true

#write a python program to demonstrate the isnumeric function.

  1. x="34567"
  2. x=str.isnumeric(x)
  3. print(x)
  4. y="123abc"
  5. y=str.isnumeric(y)
  6. priny(y)
  7. z="asd13434656"
  8. z=str.isnumeric(z)
  9. print(z)
output: true
             false
             false




 

is alpha python

 is alpha:

  • In python "is alpha" is the method used to check the alphabets whether they are present in the given string or substring.
  • In isalpha, it must carry only alphabets.
  • It carries the result in the boolean type
  • If the string contains all alphabets then it returns true, else false.
  • The isalpha is not applicable for the alphanumeric.
  • It is the built-in function of python.
syntax: str.isalpha()

Example:  s="abcdefg"
                   str.isalpha(s)
                    true

#write a python program to demonstrate is alpha function.

  1. a="india"
  2. b="india123"
  3. a=str.isalpha(a)
  4. b=str.isalpha(b)
  5. print(a)
  6. print(b)
output: true
             false


is digit python

is digit() python:  

  • The isdigit()  in python is defined as the string that consists of only digit values. 
  • It returns the result in boolean type if the string has only digits it returns true else false.
  • It accepts the Unicode of that characters also. and also the exponents like ^2.
  • It is not applicable to whitespace, special symbols, alphabets.
Syntax: str.isdigit().

Example:  str="123456"
                 str.isdigit(str) retrns true
Beacuse "123456" is perfectly a digit.
               str=\u00B0
               str.isdigit(str)returns true
Because it takes the Unicode as digit characters.

#write a python code  to demonstrate isdigit() function.

  1. a="7656734"
  2. a=str.isdigit(a)
  3. print(a)
  4. b="2344.60 
  5. b=str.isdigit(b)
  6. print(b)
  7. x="\u00B2"
  8. x=str.isdiigt(x)
  9. print(x)
output: true
            false
            true

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