Flow Control

IF Statements

If statements are similar to other languages:

if (condition)
{
    //do something
}
else if
{
    //another option
}
else 
{
    //else
}

However, in C if inside any condition there is just one line of code, the { } are optional

if (condition)
    //do something
else
    //else

Logical Operators and Comparison

== : used for equality check.
!= : not equal
>
<
>=
<=
&& AND
|| OR

Switch Case Statement

C also allows the use of switch case statements:

switch(variable)
{
    case value1:
        //do something
        break;
    case value2:
        //do something
        break;
    default:
        //do something
}

It important to know that:

The expression to switch on should be of int type (int, char,enum, etc.)
The values in the cases have to be constant
Switch case in C falls through, so using breaks is necessary but similar cases can also be stacked

While Loop

Similar to other languages, just accepts a condition

int x = -10;
while(x <= 10)
{
    printf("%d\n",x);
    x += 2;
}

while(1) is for an infinite loop

Do While Loop

Similar to the while loop but executes first and then checks the condition. So always executes at least once

char letter = 'A';
do
{
    printf("%c\n",letter);
    letter++;
}
while(letter != 'Z');

For loop

Similar to other languages, includes:

Initialization
Looping Condition
Accumulation

for(int i = 1; i <= 20; i++)
{
    printf("%d\n",i);   
}

Break and Continue

The break statement ends the loop immediately when it is encountered. Its syntax is:

break;

The continue statement skips the current iteration of the loop and continues with the next iteration. Its syntax is:

continue;

C `goto` Statement

The goto statement allows us to transfer control of the program to the specified label.

Syntax of goto Statement:

goto label;
... .. ...
... .. ...
label: 
statement;

The label is an identifier. When the goto statement is encountered, the control of the program jumps to label: and starts executing the code.

Example:

// Program to calculate the sum and average of positive numbers // If the user enters a negative number, the sum and average are displayed.

#include <stdio.h>

int main() {

   const int maxInput = 100;
   int i;
   double number, average, sum = 0.0;

   for (i = 1; i <= maxInput; ++i) {
      printf("%d. Enter a number: ", i);
      scanf("%lf", &number);
      
      // go to jump if the user enters a negative number
      if (number < 0.0) {
         goto jump;
      }
      sum += number;
   }

jump:
   average = sum / (i - 1);
   printf("Sum = %.2f\n", sum);
   printf("Average = %.2f", average);

   return 0;
}

Output:

1. Enter a number: 3
2. Enter a number: 4.3
3. Enter a number: 9.3
4. Enter a number: -2.9
Sum = 16.60
Average = 5.53

Important is that:

The use of goto statement may lead to code that is buggy and hard to follow.
Also, the goto statement allows you to do bad stuff such as jump out of the scope.
That being said, goto can be useful sometimes. For example: to break from nested loops.
goto is rarely useful and you can create any C program without using goto altogether.