Added information about scanf

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src/chapter2/scanf.md

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+# Scanf()
+In C programming language, scanf is a function that stands for Scan Formatted String. It is used to read data from stdin (standard input stream i.e. usually keyboard) and then writes the result into the given arguments.
+
+It accepts character, string, and numeric data from the user using standard input.
+scanf also uses format specifiers like printf.
+## scanf Syntax
+The syntax of scanf() in C is similar to the syntax of printf().
+
+int scanf( const char *format, ... );
+Here,
+
+int is the return type.
+format is a string that contains the format specifiers(s).
+“…” indicates that the function accepts a variable number of arguments.
+## Example format specifiers recognized by scanf:
+
+%d to accept input of integers.
+
+%ld to  accept input of long integers
+
+%lld to accept input of long long integers
+
+%f to accept input of real number.
+
+%c to accept input of character types.
+
+%s to accept input of a string.
+
+To know more about format specifiers, refer to this article – Format Specifiers in C
+
+## Example:
+
+int var;
+scanf(“%d”, &var);
+
+The scanf will write the value input by the user into the integer variable var.
+
+Return Value of scanf
+The scanf in C returns three types of values:
+
+ 1)>0: The number of values converted and assigned successfully.<br>
+ 2)0: No value was assigned.<br>
+ 3)<0: Read error encountered or end-of-file(EOF) reached before any assignment was made.<br>
+
+Why &?
+While scanning the input, scanf needs to store that input data somewhere. To store this input data, scanf needs to known the memory location of a variable. And here comes the ampersand to rescue.
+
+& is also called as address of the operator.
+For example, &var is the address of var.
+## Example of scanf
+Below is the C program to implement scanf:
+
+
+// C program to implement
+// scanf
+#include <stdio.h>
+
+int main()
+{
+    int a, b, c;
+    printf("Enter the first value:");
+    scanf("%d", &a);
+    printf("Enter the second value:");
+    scanf("%d", &b);
+    c = a + b;
+    printf("%d + %d = %d\n", a, b, c);
+    return 0;
+}
+
+//Output:
+Enter the first value:58
+Enter the second value:12
+58 + 12 = 70
+
+
+...Program finished with exit code 0
+