Question

C语言编一个程序求 1+12+123+1234+。。。+N（0〈N〈10）

Answer 1

#include"stdio.h"
void main()
{
int a[9]={1,12,123,1234,12345,123456,1234567,12345678,123456789};
int n,ans=0;
printf("Input a number N(0<N<10):");
scanf("%d",&n);
while(n<=0||n>=10)
{
printf("A wrong number ! Input N again :");
scanf("%d",&n);
}
for(int i=0;i<n;i=i+1)
ans=ans+a[i];
printf("\nThe answer is :%d\n",sum);
}

Answer 2

/*
01, 1
02, 13
03, 136
04, 1370
05, 13715
06, 137171
07, 1371738
08, 13717416
09, 137174205
Press any key to continue
*/
#include <stdio.h>
unsigned Sum(unsigned n) {
unsigned i,num = 0,sum = 0;
if(n > 9) n = 9;
for(i = 1; i <= n; ++i) {
num = 10 * num + i;
sum += num;
}
return sum;
}
int main() {
int i;
for(i = 1;i < 10;i++)
printf("%02d, %d\n",i,Sum(i));
return 0;
}

Answer 3

#include "stdio.h"
int main()
{
unsigned int num=0,sum=0;

for(int i=0;i<9;i++)
{
num = num * 10 + (i+1);
printf("%d\n",num);
sum+=num;
}

printf("\n");
printf("1+12+123+1234+...N（0<N<10）=%d\n",sum);
return 0;
}