programs written here are compiled and run in gcc (Ubuntu 7.3.0-27ubuntu1~18.04) 7.3.0 

1) Write a program to display “Hello World” in C.

Source Code:

#include<stdio.h>

int main(){
    printf("Hello World");
    return 0;
} 

Output:

Hello World

2) Write a program to add two numbers (5 and 7) and display its sum.

Source Code:

#include<stdio.h>

int main()
{
    int x = 5, y = 7, sum;
    sum = x + y;
    printf("SUM = %d", sum);
    return 0;
}

Output:

SUM = 12

3) Write a program to multiply two numbers (30 and 40) and display its products

Source Code:

#include<stdio.h>


int main()
{
    int x = 30, y = 40, product;
    product = x * y;
    printf("PRODUCT = %d", product);
    return 0;
}

Output:

PRODUCT = 1200

4) Write a program to calculate the total surface area of the sphere having its radius (r = 10 cm) and display the total surface area.

Source Code:

#include<stdio.h>
#define PI 3.1416

int main()
{
    float area, radius = 10;
    area = 4 * PI * radius * radius;
    printf("Total surface area = %f sq. cm", area);
    return 0;
} 

Output:

Total surface area = 1256.640015 sq. cm 

5) Write a program to calculate the simple interest of the given principle = 5000, rate = 5.5, time = 3.

Source Code:

#include<stdio.h>

int main()
{
    float principle = 5000, rate = 5.5, time = 3, simple_interest;
    simple_interest = (principle * time * rate) / 100;
    printf("Simple Interest = %f", simple_interest);
    return 0;
} 

Output:

Simple Interest = 825.000000 

6) Write a program to find the discounted price of shoes with tag price = 5000, discount = 15 percent.

Source Code:

#include<stdio.h>

int main()
{
    float tag_price = 5000, discount = 15, discounted_price;
    discounted_price = tag_price - tag_price * discount / 100;
    printf("Discounted Price = %f", discounted_price);
    return 0;
}

Output:

Discounted Price = 4250.000000 

7) Write a program to find the area of triangle having sides 13cm, 12 cm and 9cm.(Use math.h library to find the square root i.e. double sqrt(double num)

Source Code:

#include<stdio.h>
#include<math.h>

int main()
{
    float side1 = 13, side2 = 12, side3 = 9, area, sp;
    sp = (side1 + side2 + side3)/2;
    area = sqrt(sp * (sp - side1) * (sp - side2) * (sp - side3));
    printf("Area of Triangle = %f", area);
    return 0;
}

Output:

Area of Triangle = 52.153618