要使用C語言實現復數的加減乘除，可以先定義一個結構體表示復數，然后編寫相應的函數來進行運算。

以下是一個示例：

#include <stdio.h>

// 定義復數結構體
typedef struct {
    double real;     // 實部
    double imaginary;  // 虛部
} Complex;

// 復數加法
Complex add(Complex a, Complex b) {
    Complex result;
    result.real = a.real + b.real;
    result.imaginary = a.imaginary + b.imaginary;
    return result;
}

// 復數減法
Complex subtract(Complex a, Complex b) {
    Complex result;
    result.real = a.real - b.real;
    result.imaginary = a.imaginary - b.imaginary;
    return result;
}

// 復數乘法
Complex multiply(Complex a, Complex b) {
    Complex result;
    result.real = a.real * b.real - a.imaginary * b.imaginary;
    result.imaginary = a.real * b.imaginary + a.imaginary * b.real;
    return result;
}

// 復數除法
Complex divide(Complex a, Complex b) {
    Complex result;
    double denominator = b.real * b.real + b.imaginary * b.imaginary;
    result.real = (a.real * b.real + a.imaginary * b.imaginary) / denominator;
    result.imaginary = (a.imaginary * b.real - a.real * b.imaginary) / denominator;
    return result;
}

// 測試函數
int main() {
    Complex a = {1.0, 2.0};
    Complex b = {3.0, 4.0};

    Complex sum = add(a, b);
    printf("Sum: %lf + %lfi\n", sum.real, sum.imaginary);

    Complex difference = subtract(a, b);
    printf("Difference: %lf + %lfi\n", difference.real, difference.imaginary);

    Complex product = multiply(a, b);
    printf("Product: %lf + %lfi\n", product.real, product.imaginary);

    Complex quotient = divide(a, b);
    printf("Quotient: %lf + %lfi\n", quotient.real, quotient.imaginary);

    return 0;
}

這個示例中，我們使用了一個結構體來表示復數，包含了實部和虛部。然后，我們編寫了四個函數來分別實現復數的加法、減法、乘法和除法。在主函數中，我們定義了兩個復數a和b，并通過這四個函數進行了加減乘除運算，并打印了結果。

注意，這只是一個簡單的示例，實際情況中可能需要更多的錯誤處理和邊界情況的考慮。