In this article, you will learn to use scanf() function to take input from the user, and printf() function to display output to the user. C Output In C programming, printf() is one of the main output function. The function sends formatted output to the screen. For example, #include int main() { // Displays the string inside quotations printf("C Programming"); return 0; } How does this program work? All valid C programs must contain the main() function. The code execution begins from the start of the main() function. 
                  The printf() is a library function to send formatted output to the screen. The function prints the string inside quotations. To use printf() in our program, we need to include stdio.h header file using the #include statement. The return 0; statement inside the main() function is the "Exit status" of the program. It's optional. Example 2: Integer Output #include int main() { int testInteger = 5; printf("Number = %d", testInteger); return 0; } Output Number = 5 We use %d format specifier to print int types. Here, the %d inside the quotations will be replaced by the value of testInteger. Example 3: float and double Output #include int main() { float number1 = 13.5; double number2 = 12.4; printf("number1 = %f\n", number1); printf("number2 = %lf", number2); return 0; } Output number1 = 13.500000 number2 = 12.400000 To print float, we use %f format specifier.
                 Similarly, we use %lf to print double values. Example 4: Print Characters #include int main() { char chr = 'a'; printf("character = %c", chr); return 0; } Output character = a To print char, we use %c format specifier. C Input In C programming, scanf() is one of the commonly used function to take input from the user. The scanf() function reads formatted input from the standard input such as keyboards. Example 5: Integer Input/Output #include int main() { int testInteger; printf("Enter an integer: "); scanf("%d", &testInteger); printf("Number = %d",testInteger); return 0; } Output Enter an integer: 4 Number = 4 Here, we have used %d format specifier inside the scanf() function to take int input from the user. 
                When the user enters an integer, it is stored in the testInteger variable. Notice, that we have used &testInteger inside scanf(). It is because &testInteger gets the address of testInteger, and the value entered by the user is stored in that address. Example 6: Float and Double Input/Output #include int main() { float num1; double num2; printf("Enter a number: "); scanf("%f", &num1); printf("Enter another number: "); scanf("%lf", &num2); printf("num1 = %f\n", num1); printf("num2 = %lf", num2); return 0; } Output Enter a number: 12.523 Enter another number: 10.2 num1 = 12.523000 num2 = 10.200000 We use %f and %lf format specifier for float and double respectively. 
                 Example 7: C Character I/O #include int main() { char chr; printf("Enter a character: "); scanf("%c",&chr); printf("You entered %c.", chr); return 0; } Output Enter a character: g You entered g When a character is entered by the user in the above program, the character itself is not stored. Instead, an integer value (ASCII value) is stored. And when we display that value using %c text format, the entered character is displayed. If we use %d to display the character, it's ASCII value is printed. Example 8: ASCII Value #include int main() { char chr; printf("Enter a character: "); scanf("%c", &chr); // When %c is used, a character is displayed printf("You entered %c.\n",chr); // When %d is used, ASCII value is displayed printf("ASCII value is %d.", chr); return 0; } Output Enter a character: g You entered g. ASCII value is 103. I/O Multiple Values Here's how you can take multiple inputs from the user and display them. #include int main() { int a; float b; printf("Enter integer and then a float: "); // Taking multiple inputs scanf("%d%f", &a, &b); printf("You entered %d and %f", a, b); return 0; } Output Enter integer and then a float: -3 3.4 You entered -3 and 3.400000 Format Specifiers for I/O As you can see from the above examples, we use %d for int %f for float %lf for double %c for char Here's a list of commonly used C data types and their format specifiers. Data Type Format Specifier int %d char %c float %f double %lf short int %hd unsigned int %u long int %li long long int %lli unsigned long int %lu unsigned long long int %llu signed char %c unsigned char %c long double %Lf