4. Loops and Functions

While Loop

• When we want to repeatedly execute a statement as long as a condition is met, we can use the iteration statement called as while loop.
• The while loop is used in the case where the number of iterations is not known in advance.
• In while loop, the condition is checked first then the code under while loop is executed.

1. Write a C program to convert a binary number to a decimal number.
#include <stdio.h>
int main()
{
    int num = 1001;
    int ans = 0, x = 1;
    while (num > 0)
    {
        ans += x * (num % 10);
        x *= 2;
        num = num / 10;
    }
    printf("%d", ans);
    return 0;
}

Do-while Loop

• Do-while loop is similar to a while loop expect for the fact that it is guaranteed to execute at least once.
• After executing a part of a program for once, the rest of the code gets executed on the basis of a Boolean condition.

1. What is the output of the following C code?
#include <stdio.h>
int main()
{
    int i = 11;
    do
    {
        printf("%d ", i);
        i++;
    } while (i <= 10);
    return 0;
}

11

For Loop

• For loop is used when the exact number of iterations needed is already known to us.
• Syntax of for loop consists of 3 expressions:
• Initializer: Initializes the value of a variable. This part is executed only once.
• Checking_Boolean_Expression: The code inside the for loop is executed only when this condition returns true.
• Update: Updates the value of the previous initial value.

1. Write a C program to print first 10 elements of Fibonacci series.
#include <stdio.h>
int main()
{
    int num = 10, i;
    int a = 0, b = 1, c;
    printf("%d %d", a, b);
    for (i = 2; i < num; i++)
    {
        c = a + b;
        printf(" %d", c);
        a = b;
        b = c;
    }
    return 0;
}

Functions

• A function is a block of code that performs a particular task.
• Default return type is int.
• void is used as type if do not want any return type.
• expression can be constant, variable or function call.
• return is optional and expression is also optional.
• We cannot define one function within another function, we can only call a function within another function.
• Only one value can be returned.
• printf() is a built-in function in C whose return type is int and takes character pointer as argument.