Variables and operators

In plain English

A variable is a named box in memory that stores a value. Memory is the working storage of a running program, and compilation is the step that turns your C source file into a program the computer can run. A type tells the compiler how many bytes a variable uses and how to interpret them: int holds a whole number, double holds a decimal, and char holds one character. printf prints values by matching each format specifier such as %d, %f and %c to an argument. Integer division drops the fractional part instead of rounding, and when an unsigned integer grows past its largest value it wraps around to zero in a predictable way.

Step by step

1. 1Declare an int and print it with %d.
2. 2Add a double and print it with %.2f.
3. 3Add a char and print it with %c.
4. 4Print 7 / 2 and 7 % 2 and notice the remainder.
5. 5Print UINT_MAX and UINT_MAX + 1 to watch an unsigned value wrap.

#include <stdio.h>
#include <limits.h>

int main(void) {
    int count = 7;
    double price = 19.99;
    char grade = 'A';

    printf("count = %d\n", count);
    printf("price = %.2f\n", price);
    printf("grade = %c\n", grade);

    printf("7 / 2 = %d\n", 7 / 2);
    printf("7 %% 2 = %d\n", 7 % 2);

    unsigned int big = UINT_MAX;
    printf("UINT_MAX = %u\n", big);
    printf("UINT_MAX + 1 = %u\n", big + 1);

    return 0;
}

Common mistakes

• Using %d for a double makes printf read the wrong number of bytes and print garbage.
• Expecting 7 / 2 to be 3.5 is wrong, because integer division truncates toward zero.
• Forgetting the format specifier and printing a raw variable passes the value where printf expects a string.
• Assuming a signed integer that overflows wraps neatly is wrong, because signed overflow is undefined behaviour.