C Basics

Write a C program to swap the values of two variables using a third variable

Description: Take two numbers as input and swap their values using a third variable.

Hint:

• Save the first value in a temporary variable, then copy the second into the first, and last put the temporary value in the second.

C program to swap two numbers using a third variable

#include <stdio.h>

int main(void) {
    int a, b, temp;

    printf("Enter two numbers: ");
    scanf("%d %d", &a, &b);

    temp = a;
    a = b;
    b = temp;

    printf("After swapping: a = %d, b = %d\n", a, b);
    return 0;
}

Output:

How it works

• temp = a saves 10, a = b makes a = 20, and b = temp makes b = 10.
• Without temp the first value would be lost.

Write a C program to print words using spacing and new line characters

Description: Print the words Learn, C and Programming in a new line each, and then in one line with tab spaces.

Hint:

• Use \n for a new line and \t for a tab space.

C program to print words with escape sequences

#include <stdio.h>

int main(void) {
    printf("Learn\nC\nProgramming\n");
    printf("Learn\tC\tProgramming\n");
    return 0;
}

Output:

How it works

• One printf() can print many lines. We only write \n where the new line is needed.
• \t adds a horizontal tab between the words.

Read C Escape Sequences.

Write a C program to get the salary from the user and print it

Description: Ask the user to enter a salary. Store it in a variable and print it on the screen.

Hint:

• Use a float variable and the %f format specifier.

C program to read and print the salary

#include <stdio.h>

int main(void) {
    float salary;

    printf("Enter the salary: ");
    scanf("%f", &salary);
    printf("Your salary is %.2f\n", salary);
    return 0;
}

Output:

How it works

• scanf() reads the number typed by the user and stores it at the address of salary (&salary).
• %.2f prints the value with two digits after the decimal point.

Read C printf and scanf.

Write a C program to find the size of int, float, long, double and char

Description: Print the size (in bytes) of the basic data types of C.

Hint:

• Use the sizeof operator and the %zu format specifier.

C program to find the size of data types

#include <stdio.h>

int main(void) {
    printf("int    : %zu bytes\n", sizeof(int));
    printf("float  : %zu bytes\n", sizeof(float));
    printf("long   : %zu bytes\n", sizeof(long));
    printf("double : %zu bytes\n", sizeof(double));
    printf("char   : %zu byte\n", sizeof(char));
    return 0;
}

Output:

How it works

• sizeof gives the size of a type in bytes. It returns the type size_t, which is printed with %zu.
• The sizes can change on a different computer. For example, long is 4 bytes on 64 bit Windows. This output is from a 64 bit Mac.

Read C Data Types.

Write a C program to get the marks of 5 subjects and find the total and average

Description: Take the marks of 5 subjects as input. Print the total and the average.

Hint:

• Average is total / 5. Use float so the decimal part is not lost.

C program to find total and average marks

#include <stdio.h>

int main(void) {
    int m1, m2, m3, m4, m5, total;
    float average;

    printf("Enter marks of 5 subjects: ");
    scanf("%d %d %d %d %d", &m1, &m2, &m3, &m4, &m5);

    total = m1 + m2 + m3 + m4 + m5;
    average = total / 5.0f;

    printf("Total = %d\n", total);
    printf("Average = %.2f\n", average);
    return 0;
}

Output:

How it works

• The 5 values are read with one scanf().
• We divide by 5.0f (a float), so the result keeps its decimal part. With 5 the division would be an integer division.

Read C Type Casting.

Write a C program to calculate the perimeter of a rectangle

Description: Take the height and width of a rectangle as input, and print its perimeter.

Hint:

• Perimeter = 2 x (height + width).

C program to calculate the perimeter of a rectangle

#include <stdio.h>

int main(void) {
    float height, width, perimeter;

    printf("Enter height and width: ");
    scanf("%f %f", &height, &width);

    perimeter = 2 * (height + width);
    printf("Perimeter = %.2f\n", perimeter);
    return 0;
}

Output:

How it works

• The user enters the height and width.
• We use the formula 2 * (height + width) and print the result.

Write a C program to convert minutes into hours and minutes

Description: Take the total minutes from the user, and print how many hours and minutes it is.

Hint:

• Hours = minutes / 60 (integer division). Remaining minutes = minutes % 60.

C program to convert minutes to hours and minutes

#include <stdio.h>

int main(void) {
    int total, hours, minutes;

    printf("Enter minutes: ");
    scanf("%d", &total);

    hours = total / 60;
    minutes = total % 60;
    printf("%d minutes = %d hours and %d minutes\n", total, hours, minutes);
    return 0;
}

Output:

How it works

• 135 / 60 is 2 (integer division), so there are 2 full hours.
• 135 % 60 is 15, the minutes which are left.

Read C Operators.

Write a C program to calculate the sum of three numbers

Description: Take three numbers as input and print their sum.

Hint:

• Read the numbers with scanf() and add them with the + operator.

C program to calculate the sum of three numbers

#include <stdio.h>

int main(void) {
    int a, b, c;

    printf("Enter three numbers: ");
    scanf("%d %d %d", &a, &b, &c);

    printf("Sum = %d\n", a + b + c);
    return 0;
}

Output:

How it works

• The three numbers are stored in a, b and c.
• The expression a + b + c is calculated and printed.

Write a C program to calculate the area of a square

Description: Take the side of a square as input and print its area.

Hint:

• Area of a square = side x side.

C program to calculate the area of a square

#include <stdio.h>

int main(void) {
    float side, area;

    printf("Enter the side: ");
    scanf("%f", &side);

    area = side * side;
    printf("Area = %.2f\n", area);
    return 0;
}

Output:

How it works

• The side is read as a float, so decimal values also work.
• The area is side * side, and %.2f prints two decimal digits.

Write a C program to convert Celsius to Fahrenheit

Description: Take a temperature in Celsius and print it in Fahrenheit.

Hint:

• Fahrenheit = (Celsius x 9 / 5) + 32. Write 9.0 / 5 to avoid integer division.

C program to convert Celsius to Fahrenheit

#include <stdio.h>

int main(void) {
    float celsius, fahrenheit;

    printf("Enter temperature in Celsius: ");
    scanf("%f", &celsius);

    fahrenheit = celsius * 9.0f / 5 + 32;
    printf("%.1f C = %.1f F\n", celsius, fahrenheit);
    return 0;
}

Output:

How it works

• 37 * 9.0 / 5 is 66.6, and adding 32 gives 98.6.
• If we write 9 / 5 with integers, the result is 1 and the answer is wrong.

Read C Type Casting.

Write a C program to convert centimeters to meters and kilometers

Description: Take a length in centimeters and print it in meters and kilometers.

Hint:

• 1 meter = 100 cm and 1 kilometer = 100000 cm.

C program to convert centimeters to meters and kilometers

#include <stdio.h>

int main(void) {
    float cm, meter, km;

    printf("Enter length in cm: ");
    scanf("%f", &cm);

    meter = cm / 100;
    km = cm / 100000;
    printf("Meters = %.2f\n", meter);
    printf("Kilometers = %.5f\n", km);
    return 0;
}

Output:

How it works

• We divide the centimeters by 100 to get meters, and by 100000 to get kilometers.
• The variables are float, so the decimal part is not lost.

Write a C program to calculate 5% DA of a salary

Description: Take the basic salary as input. Calculate 5% DA on it and print the DA and the total salary.

Hint:

• DA = salary x 5 / 100.

C program to calculate the DA of a salary

#include <stdio.h>

int main(void) {
    float salary, da, total;

    printf("Enter basic salary: ");
    scanf("%f", &salary);

    da = salary * 5 / 100;
    total = salary + da;

    printf("DA = %.2f\n", da);
    printf("Total salary = %.2f\n", total);
    return 0;
}

Output:

How it works

• 5% of 20000 is 20000 * 5 / 100 = 1000.
• The total salary is the basic salary plus the DA.

Write a C program to convert the obtained marks into percentage

Description: Take the obtained marks and the total marks as input. Print the percentage.

Hint:

• Percentage = (obtained marks / total marks) x 100.

C program to calculate the percentage

#include <stdio.h>

int main(void) {
    float obtained, total, percentage;

    printf("Enter obtained marks and total marks: ");
    scanf("%f %f", &obtained, &total);

    percentage = obtained / total * 100;
    printf("Percentage = %.2f%%\n", percentage);
    return 0;
}

Output:

How it works

• 432 / 500 * 100 is 86.4.
• To print the percent sign with printf() we write %%.

Write a C program to calculate the total marks of three subjects

Description: Take the marks of three subjects and print the total and the average.

Hint:

• Total = sum of the three marks. Average = total / 3.

C program to calculate the total marks

#include <stdio.h>

int main(void) {
    int maths, science, english, total;

    printf("Enter marks of 3 subjects: ");
    scanf("%d %d %d", &maths, &science, &english);

    total = maths + science + english;
    printf("Total = %d\n", total);
    printf("Average = %.2f\n", total / 3.0);
    return 0;
}

Output:

How it works

• The marks are added to get the total.
• We divide by 3.0 to get a decimal average.

Write a C program to print your name, city and mobile number

Description: Print your name, city and mobile number on separate lines.

Hint:

• Use printf() and the new line character \n.

C program to print name, city and mobile number

#include <stdio.h>

int main(void) {
    printf("Name: Robin Sharma\n");
    printf("City: Delhi\n");
    printf("Mobile: 9876543210\n");
    return 0;
}

Output:

How it works

• Each printf() prints one line of text.
• \n moves the cursor to the next line.

Read C printf and scanf and Escape Sequences.