Practice C right here — no installs, no signups.
C is the language operating systems, embedded firmware and every other language's runtime are written in. Learning it teaches you what a pointer actually is and where memory comes from. This online C compiler compiles and links your program, then prints the program output and any compiler diagnostics.
Use it to practise pointers and arrays, structs, dynamic allocation with malloc/free, string handling with the standard library, and file-free input via scanf. Compiler warnings are shown too — reading them is half of learning C.
Copy any snippet into the editor above and press Run. Each one is short on purpose — retype it from memory afterwards.
#include <stdio.h>
int main(void) {
int nums[4] = {10, 20, 30, 40};
int *p = nums;
for (int i = 0; i < 4; i++)
printf("%d at %p\n", *(p + i), (void *)(p + i));
return 0;
}An array name decays to a pointer to its first element, so *(p + i) is exactly nums[i].
#include <stdio.h>
#include <string.h>
struct Student { char name[20]; int marks; };
int main(void) {
struct Student s;
strcpy(s.name, "Aarav");
s.marks = 78;
printf("%s scored %d\n", s.name, s.marks);
return 0;
}Strings in C are char arrays — you copy them with strcpy, not with =.
warning: implicit declaration of function 'printf'
Why: The header that declares the function was not included.
Fix: Add #include <stdio.h> at the top.
Segmentation fault
Why: You dereferenced an invalid or freed pointer, or wrote past the end of an array.
Fix: Check array bounds and confirm every pointer is assigned before use.
error: expected ';' before '}' token
Why: A missing semicolon on the previous statement.
Fix: C needs a semicolon after every statement — look at the line above the reported one.
| Concept | Syntax |
|---|---|
| Entry point | int main(void) { return 0; } |
| Print an int | printf("%d\n", x); |
| Read an int | scanf("%d", &x); |
| Pointer | int *p = &x; |
| Allocate | int *a = malloc(n * sizeof(int)); |
| Struct | struct P { int x; }; |
A modern C compiler is used, so C99/C11 features such as declaring loop variables inside for work.
Either you never called printf, or the program crashed before reaching it — check the diagnostics panel for a segmentation fault.
Running snippets builds speed; the 17-chapter course builds understanding. Work through the C chapters, take the quiz, then claim your certificate.
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