Foundations

Hello C

Start with a tiny C program that stores a name and prints a greeting.

main `main` is the function where a C program starts running.
printf `printf` writes formatted text to standard output.

Hello C

name
hello.c
Replay: real traced execution (multi-file project)
#include <stdio.h>

int main(void) {
    const char *name = "C";
    printf("Hello, %s!\n", name);
    return 0;
}

#include <stdio.h>

int main(void) {
    const char *name = "Ada";
    printf("Hello, %s!\n", name);
    return 0;
}

#include <stdio.h>

int main(void) {
    const char *name = "Dennis";
    printf("Hello, %s!\n", name);
    return 0;
}

  1. name ← C

    3int main(void) {4    const char *name→ C = "C"; //@name="Ada", "Dennis"5    printf("Hello, %s!\n", nameC);6    return 0;7}
    outputHello, C!

  1. name ← Ada

    3int main(void) {4    const char *name→ Ada = "Ada";5    printf("Hello, %s!\n", nameAda);6    return 0;7}
    outputHello, Ada!

  1. name ← Dennis

    3int main(void) {4    const char *name→ Dennis = "Dennis";5    printf("Hello, %s!\n", nameDennis);6    return 0;7}
    outputHello, Dennis!

Follow the Greeting

  1. name starts as C.
  2. printf places name inside the greeting text.
  3. The message becomes Hello, C!.
  4. The program prints Hello, C!. | name | stdout | | --- | --- | | C | Hello, C! | | Ada | Hello, Ada! | | Dennis | Hello, Dennis! |

Exercise: hello.c

Reproduce Hello, C!, then use the pinned names Ada and Dennis to predict each greeting.