int max(int a,int b);
main()
{

    int x,y,2;
    intmax(int a,int b);
    printf("input two numders;\n");
    scanf("%d%d",&x,&y);
    z=max(x,y);
    printf(maxmum=%d"z);

}

int max(int a,int b)
{
    if(a>b)return a;else return b;
}

--------------------Configuration: Hello warld - Win32 Debug--------------------
Compiling...
Hello warld.c
C:\桌面\Hello warld\Hello warld.c(5) : error C2059: syntax error : 'constant'
C:\桌面\Hello warld\Hello warld.c(6) : warning C4013: 'intmax' undefined; assuming extern returning int
C:\桌面\Hello warld\Hello warld.c(6) : error C2143: syntax error : missing ')' before 'type'
C:\桌面\Hello warld\Hello warld.c(6) : error C2059: syntax error : ')'
C:\桌面\Hello warld\Hello warld.c(7) : warning C4013: 'printf' undefined; assuming extern returning int
C:\桌面\Hello warld\Hello warld.c(8) : warning C4013: 'scanf' undefined; assuming extern returning int
C:\桌面\Hello warld\Hello warld.c(9) : error C2065: 'z' : undeclared identifier
C:\桌面\Hello warld\Hello warld.c(10) : error C2065: 'maxmum' : undeclared identifier
C:\桌面\Hello warld\Hello warld.c(10) : error C2059: syntax error : '%'
C:\桌面\Hello warld\Hello warld.c(10) : error C2001: newline in constant
C:\桌面\Hello warld\Hello warld.c(16) : error C2181: illegal else without matching if
C:\桌面\Hello warld\Hello warld.c(16) : error C2065: 'b' : undeclared identifier
执行 cl.exe 时出错.

Hello warld.obj - 1 error(s), 0 warning(s)

int max(int a,int b);
main()
{

    int x,y,z;
    int max(int a,int b);
    printf("input two numders;\n");
    scanf("%d%d",&x,&y);
    z=max(x,y);
    printf("maxmum=%d",z);

}

int max(int a,int b)
{
    if(a>b)return a;else return b;
}

int max(int a,int b);
main()
{

    int x,y,z;
    int max(int a,int b);
    printf("input two numders;\n");
    scanf("%d%d",&x,&y);
    z=max(x,y);
    printf("maxmum=%d",z);

}

int max(int a,int b)
{
    if(a>b)return a;else return b;
}

intmax(int a,int b);       \Hello warld\Hello warld.c(6) : warning C4013: 'intmax' undefined; assuming extern returning int
编完看错误提示 啊，自己试试改

#include<stdio.h>

int max(int a,int b);
main()
{

    //int x,y,2;                               //z写成2了
    int x,y,z;
    //intmax(int a,int b);                    //这句用来做什么？
    printf("input two numders;\n");
    scanf("%d%d",&x,&y);
    z=max(x,y);
    printf("maxmum=%d\n", z);                  

    return 0;                                  //要有return

}
int max(int a,int b)
{
    if(a>b)
        return a;
    else
        return b;
}

# include <stdio.h>
int max(int a,int b);
main()
{

    int x,y,z;//你这写错了吧
    int max(int a,int b);//数据类型跟调用函数得分开
    printf("input two numders;\n");
    scanf("%d%d",&x,&y);
    z=max(x,y);
    printf("maxmum=%d",z);//缺少双引号

}

int max(int a,int b)
{
    if(a>b)return a;else return b;
}

int x,y,2;
首先你这里，常量2，我感觉应该是z吧？
 intmax(int a,int b);
你这里int max 之间要有空格
 printf(maxmum=%d"z);
你这个少了个逗号，前面少了个双引号： printf("maxmum=%d",z);
新手吧？马马虎虎

友情提示：看书，学习！！！！

先把书上的程序打几遍记住那些常用的指令格式，就会好很多了！