01 C program to print "hello world".

#include<stdio.h>

int main(){

    printf("Hello world");

    return 0;

}

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02 C program to add two numbers in c.

#include<stdio.h>

int main(){

    int a,b,sum;

    scanf("%d %d",&a,&b);

    sum = a + b;

    printf("%d",sum);

    return 0;

} 

 

 

03 C program to accept a string from users and print it.

#include<stdio.h>

int main(){

    char str[20];

    scanf("%s",&str);

    printf("%s",str);

    return 0;

}

 

04 C program to check a given number is positive or negative. 

#include<stdio.h>

int main(){

    int num;

    scanf("%d",&num);

   

    if(num ==0)

         printf("Number is zero.");

    else if(num > 0)

printf("Number is positive.");

else

printf("Number is negative.");

    return 0;

}

 

05 C program to swap two numbers.

#include<stdio.h>

int main(){

    int a,b,c;

    scanf("%d %d",&a,&b);

   

    c = a;

    a = b;

    b = c;

    printf("%d %d",a,b);

    return 0;

}

06 C program to find area of a circle.

#include<stdio.h>

int main(){

    floar r,area;

        

    printf("Enter radius of circle: ");

    scanf("%f",&r);

    area = 3.14 * r * r;

    printf("Area of circle is: %f",area);

    return 0;

}