C - Programming Guide

ans="y"
while [ $ans = "y" ]    #loops till answer is yes
do
  echo "-----MENU-----"    #prints menu
  echo "1.Factorial of number"
  echo "2.Greatest number of 3"
  echo "3.Prime number or not"
  echo "4.number is palindrome or not"
  echo "5.string is palindrome or not"
  echo "6.Exit"
  echo –n "enter your choice :"   
  read ch    #reads users choice
  case $ch in
  1)echo –n  "Enter a number: "
     read num
     i=2
     res=1
     if [ $num -ge 2 ]
     then
        while [ $i -le $num ] #calculates factorial of given number
        do
            res=`expr $res \* $i`
            i=`expr $i + 1`
       done
   fi
   echo "Factorial of $num = $res"
   ;;
  2)echo –n "Enter the 1st number :"
     read num1
     echo –n "Enter the 2nd number :"
     read num2
     echo –n "Enter the 3rd number :"
     read num3
     if [ $num1 -gt $num2 ] && [ $num1 -gt $num3 ]    #compare 3

numbers
     then
         echo "$num1 is biggest number!!!"
    elif  [ $num2 -gt $num3 ]
    then
        echo "$num2 is biggest number!!!"
    else
        echo "$num3 is biggest number!!!"
    fi
    ;;
  3)i=2
     flag=0
     echo –n "Enter the number :"
     read num
     while [ $i -lt `expr $num - 1` ]    #check whether number is prime
     do
        if [ `expr $num % $i` = 0 ]
        then
          flag=1    #if number is prime sets the flag
        fi
       i=`expr $i + 1`
    done
     if [ $flag = 1 ]
     then
        echo "$num is not prime."
    else
       echo "$num is prime."
    fi
    ;;
  4)l=0
    cnt=1
    tag=0
    echo –n "Enter a number :"
    read num
    l=`echo $num|wc -c`
    l=`expr $l - 1`
    lh=`expr $l / 2`
    while [ $cnt -le $lh ]    #loops till half length of number
    do
        c1=`echo $num|cut -c $cnt`
        c2=`echo $num|cut -c $l`
        if [ $c1 != $c2 ]    #compare first and last number
        then
            cnt=$lh
            tag=1
        fi
        cnt=`expr $cnt + 1`
        l=`expr $l - 1`
    done
    if [ $tag -eq 0 ]
    then
        echo "Number is Palindrome"
    else
       echo “Number is not Palindrome”
    fi
    ;;
  5)l=0
    cnt=1
    tag=0
    echo –n "Enter a String :"
    read str
    l=`echo $str|wc -c`
    l=`expr $l - 1`
    lh=`expr $l / 2`
    while [ $cnt -le $lh ]    #ckecks whether string is palindrome
    do
       c1=`echo $str|cut -c $cnt`
       c2=`echo $str|cut -c $l`
       if [ $c1 != $c2 ]
       then
             cnt=$lh
            tag=1
       fi
      cnt=`expr $cnt + 1`
      l=`expr $l - 1`
   done
    if [ $tag -eq 0 ]
    then
       echo "String is Palindrome"
    else
       echo "String is not Palindrome"
    fi
    ;;
  6)exit;;    #exit from shell script
  *)echo "Please enter correct choice !!!";;
  esac
  echo –n "Do you want to continue?"   
  read ans
done
echo "Thank you!!!"