Add tutorial printf.c (#93)

* Create printf.c

* Tidy up tutorial format

* Update printf.c

Co-authored-by: Fum <66768334+funbeedev@users.noreply.github.com>

11-common-built-in-functions/printf.c

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+/*
+---------------------------------------------------------------------------------------------------------------------------------
+ Tutorial: This tutorial is about how to use printf function in c language.
+           - Printf() is one of the primary output functions in C programming. A prepared output is sent to the screen by the function.
+           - We must use the #include <stdio.h> declaration to include the stdio.h header file in order to use printf() in our application.
+           - We use %d format specifier to print int types. %d gets replaced by the variable's value.
+           - To print float, we use %f format specifier.
+           - to print char, we use %c format specifier.
+           - To print double type , we use %lf format specifier.
+           - You can also perform some arithmetic operations in it.
+           - printf function returns the number of characters printed and negative if error occurs
+-----------------------------------------------------------------------------------------------------------------------------------
+*/
+
+#include <stdio.h>   // The "#include stdio.h>"" declaration must be used to include
+                    // the stdio.h header file if we want to utilise printf().
+
+int main() {  // The main function
+  // print whole string using double quotation marks ("").
+  printf("Hello World \n");  // \n is used for line break
+
+  // you can also print the number of element in print function
+  int x = printf("Hi github");
+  printf("\n %d \n", x);  // 9 is the output (note: the space character is counted)
+
+  // Declaring variables
+  int a = 10;
+  char c = 'c';
+  float f = 12.3;
+  double d = 15.43;
+
+  // For printing int types, we utilise the %d format specifier. The value
+  // of the variable is substituted for by %d.
+  printf("Integer a = %d \n", a);
+
+  // To print char type, %c is used.
+  printf("Character c = %c \n", c);
+
+  // To print float, we use %f format specifier.
+  printf("Float f = %f \n", f);
+
+  // To print double type, %lf is used.
+  printf("Double d = %lf \n", d);
+
+  // You can do some operation printf function and result will be displayed.
+  printf("a + d = %lf \n", a+d);
+
+  return 0;
+}
+/*
+--------------------------------------------------------------------------------------------------------------------------------------
+Challenge: Take input from user in variable a and b, print number of elements present in each variable and then print sum of number of
+            elements present in a and b.
+            example: 
+              - a = 12343212 and b = 887788
+              - number of elements in a is 8 and in b is 6.
+              - sum is 14.
+            
+
+--------------------------------------------------------------------------------------------------------------------------------------
+*/