Written: August 14, 2026
Swapping two numbers is one of the first logic drills in C: you move values between variables without losing either one.
This walkthrough keeps the logic small and readable so you can type it, run it, and then change one input at a time to see what happens.
What you will build
You will read two integers, store one in a temporary variable, then reassign so the values trade places before printing.
- Declare three integers: a, b, and temp
- Read a and b from the user
- Copy a into temp, copy b into a, copy temp into b
- Print the swapped values
Working C example
#include <stdio.h>
int main(void) {
int a, b, temp;
printf("Enter two integers: ");
if (scanf("%d %d", &a, &b) != 2) {
return 1;
}
temp = a;
a = b;
b = temp;
printf("After interchange: %d %d\n", a, b);
return 0;
}How the logic works
Read the program top to bottom: includes and main first, then the statements that change variables, then the print that proves the result.
If your output looks wrong, print the variables before and after the critical lines. That single habit catches most beginner bugs faster than rewriting the whole file.
Once the temp-variable version is clear, try the arithmetic or XOR variants for practice—but prefer the temp approach in real code for readability.
Common mistakes
Forgetting a semicolon, using the wrong format specifier in printf/scanf, and mixing up assignment (=) with comparison (==) are the usual culprits.
Compile with warnings enabled (`gcc -Wall`) so the compiler points at risky casts and unused variables before you chase them by hand.
Try this next
Change the sample inputs, add a second test case, and briefly note what stayed the same. Teaching yourself with tiny experiments sticks better than copying a longer program you never run.
When you can explain every line without looking, you are ready for the next exercise in the series.
