Before you move forward, it is important to solidify your understanding of how a basic C program is structured. In the previous example, you learned that every C program must include the `main` function, which serves as the entry point for execution. You also saw how to use the `#include <stdio.h>` directive to access input and output functions such as `printf`. Additionally, you learned that statements in C end with a semicolon, and that curly braces `{}` are used to define the body of a function. With these elements in mind, you are ready to put your knowledge into practice by writing your own C program.


#define CATCH_CONFIG_MAIN
#include <catch2/catch.hpp>

int _testmain();


void print_custom_message();

TEST_CASE("Function prints a non-empty custom message", "[print_custom_message]") {
    std::ostringstream output;
    FILE* old_stdout = stdout;
    int fds[2];
    pipe(fds);
    fflush(stdout);
    dup2(fds[1], STDOUT_FILENO);

    print_custom_message();

    fflush(stdout);
    char buffer[256] = {0};
    read(fds[0], buffer, sizeof(buffer)-1);
    dup2(fileno(stdout), STDOUT_FILENO);

    std::string printed(buffer);
    // Remove trailing newline and whitespace
    printed.erase(printed.find_last_not_of(" \\n\\r\\t") + 1);
    REQUIRE(printed.size() > 0);
    REQUIRE(printed != "Hello, World!");
}

test.cpp


#define CATCH_CONFIG_MAIN
#include <catch2/catch.hpp>

int _testmain();


void print_custom_message();

TEST_CASE("Function signature is correct (no parameters, no return)", "[print_custom_message]") {
    // Just check that the function can be called without arguments and returns void
    print_custom_message();
    REQUIRE(true); // If compilation passes, signature is correct
}


#define CATCH_CONFIG_MAIN
#include <catch2/catch.hpp>

int _testmain();


int _testmain();

TEST_CASE("Function is called from main", "[main-calls-print_custom_message]") {
    std::ostringstream output;
    FILE* old_stdout = stdout;
    int fds[2];
    pipe(fds);
    fflush(stdout);
    dup2(fds[1], STDOUT_FILENO);

    _testmain();

    fflush(stdout);
    char buffer[256] = {0};
    read(fds[0], buffer, sizeof(buffer)-1);
    dup2(fileno(stdout), STDOUT_FILENO);

    std::string printed(buffer);
    printed.erase(printed.find_last_not_of(" \\n\\r\\t") + 1);
    REQUIRE(printed.size() > 0);
}

A comprehensive introduction to the C programming language, covering essential concepts, syntax, and practical skills for beginners. This course blends clear explanations with hands-on practice to build a solid foundation in C.

Learn the basic structure of a C program and how to write your first code.

Understand how to declare variables, use different data types, and perform operations in C.

Learn how to control the flow of your C programs using conditional statements.

Master the use of loops to perform repetitive tasks efficiently in C.

Discover how to define and use functions to organize and reuse code.

Challenge: Write Your First C Program

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Challenge: Write Your First C Program

Lösning