STEP 1 Review: Variables, printf, and scanf

🦴 Program structure

#include <stdio.h>

int main(void) {
    printf("Hello\n");
    return 0;
}

• #include <stdio.h>— declares printf and scanf
• int main(void)— execution begins here
• return 0;— signals successful completion

📦 Types and format specifiers

• For double, printf uses %f; scanf uses %lf(take care!)
• Use %d for integers and %f for real numbers; do not mix them.
• Specify precision or width with %.2f(two decimal places) %5d(right-aligned in five columns), for example.

🖨️ Using printf

printf("x=%d, y=%d\n", x, y);
printf("%.2f", 3.146); // → 3.15 (rounded) 
printf("%5d", 42);   // → 42 (right-aligned in five columns) 
printf("%05d", 42);  // → 00042 (zero-padded) 

• Each conversion such as %d or %f in the format string requires a corresponding argument, in order.
• \nadds a newline; without it, output continues on the same line.

⌨️ Rules for scanf

int n;
scanf("%d", &n);   // & is required! 

double x;
scanf("%lf", &x); // Use %lf for double 

• Pass the variable's address (&) ; omitting & can cause a crash.
• For double, scanf uses %lf(unlike printf's %f).

🔁 Assignments overwrite values in order

int a = 10;  // a:10
int b = 30;  // b:30
b = a;        // b:10 (30 is overwritten) 
a = 5;        // a:5 (10 is overwritten) 
// Result: a=5, b=10 

• = means assign the right-hand value to the left-hand variable, not equality.
• A later assignment replaces the previous value