Learn what each C statement does instead of memorizing syntax. Start with small programs, follow changes in memory and control flow, then explore interactive examples.
Browse the free interactive course →C programs use declarations, expressions and statements to describe a sequence of operations. A variable such as int total = 0; stores a typed value. printf displays output, and scanf can read input when used with an appropriate format and argument.
Begin with computer programming and Hello World, then explore data types, variables and memory.
An if statement chooses whether to execute a block. A for loop repeats instructions while its condition is true. To trace a loop, write down the counter and output after every iteration.
Use the conditions module and the interactive C for-loop lesson to step forward, backward and reset the execution trace.
This program prints the numbers 1, 2 and 3. The counter is initialized once, checked before every iteration, and increased after each iteration's body.
#include <stdio.h>
int main(void) {
for (int i = 1; i <= 3; ++i) {
printf("%d\n", i);
}
return 0;
}Trace it: i = 1 prints 1; i = 2 prints 2; i = 3 prints 3; i = 4 fails the condition and the loop ends. Try predicting the output if i <= 3 becomes i < 3.
An array groups elements of one type. In C, the first element has index 0. For example, int scores[3] = {10, 20, 30}; gives scores[1] the value 20. When tracing access, check the declared length to avoid out-of-bounds operations.
Open the visual arrays lesson and practice reading and changing indexed values.
A function groups code into a reusable operation. A pointer stores the address of another object: &x produces the address of x, and *p can access the pointed-to value when the pointer is valid. Drawing values and addresses helps explain the difference.
Study functions and the interactive pointers lesson.
You can change the interface language independently of the code language. The examples are teaching simulations; for full native C execution use an appropriate compiler, or the linked online editor when offered.
Also explore our visual data structures guide.
Choose a focused visual walkthrough, then return to the main interactive course to practice more examples.