以下是一个用C语言输出菱形图案的示例代码：

#include <stdio.h>int main() {int n, c, k, space = 1;printf("Enter number of rows: ");scanf("%d", &n);space = n - 1;for (k = 1; k <= n; k++) {for (c = 1; c <= space; c++)printf(" ");space--;for (c = 1; c <= 2*k-1; c++)printf("*");printf("\n");}space = 1;for (k = 1; k <= n - 1; k++) {for (c = 1; c <= space; c++)printf(" ");space++;for (c = 1 ; c <= 2*(n-k)-1; c++)printf("*");printf("\n");}return 0;}

使用以上代码，用户输入行数后，程序会输出一个由星号组成的菱形图案。