What is the difference between while and do-while loops in C?

• Pre increment operator is used to increment variable value by 1 before assigning the value to the variable.
• Post increment operator is used to increment variable value by 1 after assigning the value to the variable.

• Pre decrement operator is used to decrement variable value by 1 before assigning the value to the variable.
• Post decrement operator is used to decrement variable value by 1 after assigning the value to the variable.

• * Operator is used as pointer to a variable. Example: * a where * is pointer to the variable a.
• & operator is used to get the address of the variable. Example: &a will give address of a.

Explanation

Practical Example

The address-of operator (&) in C is used to get the memory address of a variable. Here is an example:

#include <stdio.h>

int main() {
    int x = 5;
    printf("The memory address of x is: %p\n", &x);
    return 0;
}

In this example, the variable x is initialized with the value of 5, and the address of x is printed using the address-of operator and the %p format specifier. The output would be something like "The memory address of x is: 0x7ffc6f9a6b24"

The dereference operator * in C is used to get the value stored at a memory address. Here is an example:

#include <stdio.h>

int main() {
    int x = 5;
    int *ptr = &x;
    printf("The value of x is: %d\n", *ptr);
    return 0;
}

In this example, the variable x is initialized with the value of 5, the memory address of x is stored in ptr and finally, the value stored at the memory address of x is printed using the dereference operator * and the %d format specifier. The output would be something like "The value of x is: 5"

• Switch case statements are used to execute only specific case statements based on the switch expression.
• If we do not use break statement at the end of each case, program will execute all consecutive case statements until it finds next break statement or till the end of switch case block.

Example

If the break statement is not used in a switch case in C, the code will continue to execute the next case statement(s) after a match is found.

For example:

switch (x) {
    case 1: 
        printf("Case 1");
    case 2: 
        printf("Case 2");
    case 3: 
        printf("Case 3");
}

If the value of x is 1, the output will be "Case 1Case 2Case 3". This is because after the first match, the code continues to execute the next case statements, instead of breaking out of the switch statement with the use of the break statement.

To avoid this problem, the break statement should be used at the end of each case block.

switch (x) {
    case 1: 
        printf("Case 1");
        break;
    case 2: 
        printf("Case 2");
        break;
    case 3: 
        printf("Case 3");
        break;
}

This way, when the program reaches the matching case, it will break out of the switch statement and will not execute any other cases.

Switch case statements are used to execute only specific case statements based on the switch expression. If switch expression does not match with any case, default statements are executed by the program.

Example

int x = 3;

switch (x) {
    case 1:
        printf("x is 1");
        break;
    case 2:
        printf("x is 2");
        break;
    default:
        printf("x is not 1 or 2");
        break;
}

In this example, if x=3 which is not handled by any of the case statement, the default statement will be executed.

goto statement is used to transfer the normal flow of a program to the specified label in the program. Below is the syntax for goto statement in C.

{
                  </div>
                </div>
                        <div class="d-flex w-100 justify-content-between">
                <a style="color:#9e9d9d;" href="/tutorial/goto-statement-in-c/1/200">
                    <small># Tutorial: goto Statement in C</small> 
                </a>
            </div>
           
                        <a style="color:#9e9d9d;" href="/qa/-/1/45">
                <small><i class="fa fa-code" aria-hidden="true"></i> Question: Control Flow in C Programming </small>
            </a>
                                   <span class="float-end" style="color:#9e9d9d"> <small><i class="fa fa-check" aria-hidden="true"></i> Short </small></span>  
                            </div>
      
            <div class="list-group divStyleQuestion" style="border:1px solid #e0e0e0;padding:8px">
            <div class="d-flex w-100 justify-content-between">
              <a href="/qanswer/what-value-will-be-assigned-to-the-variable-x-if-a-10-b-20-c-30-d-40-for-the-expression-x-a-b-c-d-c-question/25/650">
                  <h5 class="mb-1" style="color:#194757;">650. &nbsp;What value will be assigned to the variable X if a = 10, b = 20, c = 30, d = 40 for the expression X = a/b+c*d-c?</h5>
              </a>
            </div>
                            <div class="card">
                  <div class="card-body">
                     Answer: <ul>
<li>The above arithmetic operation is performed based on the precedence of the operators.</li>
<li>In above mentioned expression, c*d will be performed first. Then, a/b, then (c*d)-c, then (a/b) + ((c*d)-c).</li>
<li>Please check the operator precedence table to know the priority and associativity of the C operators.</li>
<li>Output of the above expression is 1170.</li>
</ul>
<pre class="prettyprint">
<xmp>

2
3
4
5
6
7
8
9
10
11
#include <stdio.h>
#include <stdlib.h>
 
int main()
{
   int a = 10, b = 20, c = 30, d = 40, X ;
 
   X = a/b+c*d-c;
   printf(" Value of X = %d\n", X);
   return 0;
}

int X1 = 13/3;
int X2 = 13%3;

• The value of X1 is 4
• The value of X2 is 1

Storage class of all variables are auto by default unless we specify a variable is register or static or extern in C program.

• Both auto variable and register variable are local variables. Register variables are stored in register memory. Whereas, auto variables are stored in main CPU memory.
• Register variables will be accessed very faster than the normal/auto variables since they are stored in register memory rather than main memory.
• But, only limited variables can be used as register since register size is very low. (16 bits, 32 bits or 64 bits)

• Both auto and static variables are local variables.
• Static variables can retain the value of the variable between different function calls.
• But, scope of auto variable is within the function only. It can’t retain the value of the variable between different function calls.