#include <stdio.h>
#define PI 3.14159
main()
{
    float circum,totalcost,no;
    circum=area();
    totalcost=cost(circum,cost,no);
    printf("Total cost is %f\n",totalcost);
}

float area(float r, float h)
{
    printf("Input Radius:");
    scanf("%f",r);
    printf("Input Height:");
    scanf("%f",h);
    printf("Circumference of a container is %f",PI*r*r+h*2*PI*r);
    return(PI*r*r+h*2*PI*r);
}
float cost(float circum,float totalcost,float no)
{
    printf("Input Quantity:");
    scanf("%f",&no);
    printf("Input cost per cm^2:");
    scanf("%f",&cost);
    printf("Cost of each container is %f\n",circum*cost);
    totalcost=circum*cost*no;
    return(totalcost);
}

定义两个函数，area涌来计算圆柱体的表面积，cost函数计算每个圆柱体的花费和总花费，
函数调用我不怎么熟悉，请问哪里错了？谢谢。

printf("Input Quantity:");
    scanf("%f",&no);
    printf("Input cost per cm^2:");
    scanf("%f",&cost);
    printf("Cost of each container is %f\n",circum*cost);
    totalcost=circum*cost*no;
    return(totalcost);

定义的函数应先声明吧，然后在定义
要么就在main()之前就定义好，否则会提示错误的

先定义，在使用

错误真多……改了好多，不过虽然编译过了，还是不敢运行……

建议LZ好好看书……

#include <stdio.h>
#define PI 3.14159
float area(float r, float h);
float wcost(float circum,float cost,float no);
void main()
{
    float circum,totalcost,no,r,h,cost;
    printf("Input Radius:");
    scanf("%f",&r);
    printf("Input Height:");
    scanf("%f",&h);
    circum=area(r,h);

    printf("Input Quantity:");
    scanf("%f",&no);
    printf("Input cost per cm^2:");
    scanf("%f",&cost);
    totalcost=wcost(circum,cost,no);

    printf("Total cost is %f:\n",totalcost);
}

float area(float r, float h)
{

    printf("Circumference of a container is %f",PI*r*r+h*2*PI*r);
    return(PI*r*r+h*2*PI*r);
}
float wcost(float circum,float cost,float no)
{
    float totalcost;
    printf("Cost of each container is %f\n",circum*cost);
   totalcost=circum*cost*no;
    return(totalcost);
}