要用C语言绘制曲线，可以使用图形库如OpenGL或者SDL来实现。下面是一个简单的使用SDL绘制曲线的示例代码：

#include <SDL.h>int main(int argc, char *argv[]) {SDL_Init(SDL_INIT_VIDEO);SDL_Window *window = SDL_CreateWindow("Curve Drawing",SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,800, 600, 0);SDL_Renderer *renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);SDL_RenderClear(renderer);SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);int x1 = 100, y1 = 100;int x2 = 700, y2 = 500;int steps = 100;for (int i = 0; i < steps; i++) {float t = (float)i / steps;int x = x1 + t * (x2 - x1);int y = y1 + t * (y2 - y1);SDL_RenderDrawPoint(renderer, x, y);}SDL_RenderPresent(renderer);bool quit = false;SDL_Event event;while (!quit) {while (SDL_PollEvent(&event)) {if (event.type == SDL_QUIT) {quit = true;}}}SDL_DestroyRenderer(renderer);SDL_DestroyWindow(window);SDL_Quit();return 0;}

这个示例代码使用SDL库来创建窗口和渲染器，然后绘制一条直线。你可以修改x1、y1、x2、y2来绘制不同的曲线，也可以修改steps来控制曲线的平滑度。整个绘制过程是通过在起点和终点之间插值的方式来实现的。最后，通过处理SDL的事件循环来保持窗口显示，直到用户关闭窗口。