Write a C program to test whether a given identifier is valid or not

#include<stdio.h>
#include<conio.h>
#include<ctype.h>
void main()
{
    char a[10];
    int flag,
    i=1;
    clrscr();
    printf("\n Enter an identifier:");
    gets(a);
    if(isalpha(a[0]))
    flag=1;
    else
    printf("\n Not a valid identifier");
    while(a[i]!='\0')
    {
        if(!isdigit(a[i])&&!isalpha(a[i]))
        {
            flag=0; break;
           
        } i++;
       
    }
    if(flag==1)
    printf("\n Valid identifier");
    getch();
   
}

Program for DDA Line Drawing Algorithm in C

//   Program for DDA Line Drawing Algorithm in C

 

#include <graphics.h>

#include <stdio.h>

#include <math.h>

#include <dos.h>

 

void main( )

{

    float x,y,x1,y1,x2,y2,dx,dy,step;

    int i,gd=DETECT,gm;

 

    initgraph(&gd,&gm,"c:\\turboc3\\bgi");

 

    printf("Enter the value of x1 and y1 : ");

    scanf("%f%f",&x1,&y1);

    printf("Enter the value of x2 and y2: ");

    scanf("%f%f",&x2,&y2);

 

    dx=abs(x2-x1);

    dy=abs(y2-y1);

 

    if(dx>=dy)

        step=dx;

    else

        step=dy;

 

    dx=dx/step;

    dy=dy/step;

 

    x=x1;

    y=y1;

 

    i=1;

    while(i<=step)

    {

        putpixel(x,y,5);

        x=x+dx;

        y=y+dy;

        i=i+1;

        delay(100);

    }

 

    closegraph();

}

Compiler Design Program

/******************************************************************************

Write a C program to identify whether a given line is a comment or not.

*******************************************************************************/

#include<stdio.h>

#include<conio.h>

void main()

{

    char com[30];

    int i=2,a=0;

    clrscr();

    printf("\n Enter comment:");

    gets(com);

    if(com[0]=='/')

    {

        if(com[1]=='/')

    printf("\n It is a comment");

    else if(com[1]=='*')

    {

        for(i=2;i<=30;i++)

        {

            if(com[i]=='*'&&com[i+1]=='/')

            {

                printf("\n It is a comment");

                a=1;

                break;

               

            } else continue;

           

        }

        if(a==0)

        printf("\n It is not a comment");

       

    } else printf("\n It is not a comment");

       

    } else printf("\n It is not a comment");

    getch();

   

}